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Other Link： http://id.ndl.go.jp/bib/030312812

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In this study, monolayer (ML)- and superlattice (SL)-diluted magnetic GaGdAs semiconductors are fabricated, and their electronic states are analyzed by X-ray absorption spectrum (XAS) and magnetic circular dichroism (MCD) by comparing with the values observed in case of macroscopic magnetization. The Gd magnetic moment per atom that was obtained from MCD exhibited a lower value than that obtained from a superconducting quantum interference device (SQUID) and tended to be larger in the SL structure as compared to the ML structure. We further observed that the Gd magnetic moment was enhanced by more than several tens of μ B because of increasing carrier density by Si doping. The transmission electron microscopy images revealed dark regions with diameters of 2–3 nm, which were indicative of the high concentrations of Gd that further resulted in the formation of zincblend GaGdAs particles.

DOI： 10.1016/j.jmmm.2018.10.084

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DOI： 10.18926/cted/55805

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Association for Computational Linguistics  

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Other Link： https://dblp.uni-trier.de/conf/paclic/2018

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Language：Japanese   Publishing type：Research paper (bulletin of university, research institution)   Publisher：岡山大学環境管理センター  

This study is a part of the activity to develop an interdisciplinary class on the climate environment around the Japan Islands and the "seasonal feeling", succeeding to Kato et al. (2014). In the class at the Faculty of Education, Okayama University in 2014, the comparative expression of the seasonal feelings between early winter and early spring was made, with attention to the asymmetric seasonal march from autumn to the next spring pointed out by Kato et al. (2013). The students tried the expression firstly with combination of the colored papers based on the Johannes Itten's (1888-1967) exercise, next with use of the small percussion instruments, and finally with the colored papers again. Analyses of the students' works suggested the deepening of the expressions on different seasonal feelings between early winter and early spring by the interaction of the art and music activities with each other, such as the music expressions with imaging colors or superposition of the tones at the second activity, the art expressions influenced by the music works in selecting the configurations or combination of the colored papers at the third activity, and so on. It is also interesting that the students' expressions of the seasonal feelings seem to be reflected by not only the mean seasonal state but also some specified factors in the seasonal march.

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2427

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The pressure-temperature-field phase diagram and quantum fluctuation effect were investigated in the itinerant ferromagnet U3P4 by resistivity, ac susceptibility, and Hall effect measurements under high pressure. The zero-temperature ferromagnetic-to-paramagnetic transition is located at P-c similar to 4.0 GPa. The tricritical point exists at P* = 3.8 GPa and T* = 32 K, where the ferromagnetic transition changes from second- to first-order. As a quantum fluctuation effect, the low-temperature resistivity at P-c follows T-5/3 dependence, which was theoretically described in the case of a three-dimensional ferromagnet. This result indicates that the ferromagnetic-to-paramagnetic transition at P-c may be considered as weakly first-order. Another critical behavior, the huge enhancement of rho(0) observed at P-c, cannot be interpreted as the ferromagnetic fluctuation effect. The Hall effect measurements suggest that the magnetic structure in the ordered state changes under high pressure.

DOI： 10.7566/JPSJ.84.024705

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Language：Japanese   Publisher：The Physics Education Society of Japan  

DOI： 10.20653/pesj.62.4_221

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Superconductors with noncentrosymmetric crystal structures such as Li2T3B(T:Pd,Pt) have been the focus of in-depth research with their parity mixing nature. In this study, we focused our research on non-magnetic impurity effect in Li2T3B(T:Pd,Pt). The nature of the pair breaking by non-magnetic impurity in the parity mixing superconducting state is still unclear. We prepared different quality samples of Li2Pd3B and Li2Pt3B by changing conditions in synthesizing, and sample qualities were estimated by residual resistivity. Spin singlet dominant superconductor Li2Pd3B exhibits the weak T-c suppression attributed by nonmagnetic impurity and defects, while H-c2 (0) value increased. This behavior is similar in ordinary s-wave superconductor. On the other hand, for the spin triplet dominant superconductor Li2Pt3B, it was suggested that the Cooper pair was broken and superconducting gap was decreased by non-magnetic impurities and defects. Li2Pt3B is similar to unconventional superconducting state. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2013.04.059

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DOI： 10.7566/JPSJ.82.065002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report the systematic investigation of the specific heat of the noncentrosymmetric superconductor Li-2(Pd1-xPtx)(3)B as a function of x. There is a large deviation of the phononic specific heat from the conventional Debye specific heat for Pt-rich samples. In contrast with the fully gapped conventional behavior for small x, a power-law temperature dependence of the electronic specific heat is observed even at x = 0.5. These results manifest a strongly anisotropic or nodal superconducting gap even at x = 0.5 and a nodal superconducting gap for x greater than or similar to 0.9.

DOI： 10.1103/PhysRevB.87.161203

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DOI： 10.18926/CTED/49510

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We report B-11 nuclear magnetic resonance (NMR) studies of the impurity effect in noncentrosymmetric superconductors Li2Pt3B and Li2Pd3B. We substitute B with Al, and find that the full width of half maximum (FWHM) of the NMR spectrum increases with increasing Al content. The superconducting transition temperature (T-c) of Li2Pt3 B1-xAlx decreases drastically with increasing non-magnetic impurity (Al) content, while it is hardly affected in Li2Pd3 B(1-x)A(l)x. These results provide new evidence for superconducting gap with line nodes in Li2Pt3B.

DOI： 10.1088/1742-6596/449/1/012034

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We report synthesis, Pt-195, B-11, and Li-7 NMR measurements, and first-principles band calculations for noncentrosymmetric superconductors Li-2(Pd1-xPtx)(3)B (x = 0, 0.2, 0.5, 0.8, 0.84, 0.9, and 1). For 0 <= x <= 0.8, the spin-lattice relaxation rate 1/T-1 shows a clear coherence peak just below T-c, decreasing exponentially at low temperature, and the Knight shift K-195 decreases below Tc. For x = 0.9 and 1.0, in contrast, 1/T-1 shows no coherence peak but a T-3 variation and K-195 remains unchanged across T-c. These results indicate that the superconducting state changes drastically from a spin-singlet dominant to a spin-triplet dominant state at x = 0.8. We find that the distortion of B(Pt,Pd)(6) increases abruptly above x = 0.8, which leads to an abrupt enhancement of the asymmetric spin-orbit coupling as confirmed by band calculation. Such structure distortion that enhances the extent of inversion-symmetry breaking is primarily responsible for the pairing symmetry evolution. The insight obtained here provides a guideline for searching for noncentrosymmetric superconductors with a large spin-triplet component.

DOI： 10.1103/PhysRevB.86.220502

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Using an ac susceptometry technique, H-T phase diagrams were determined for various Pt contents in the noncentrosymmetric superconducting system Li-2(Pd1-xPtx)(3)B, from which several superconducting parameters could be extracted. Despite the end compositions having very different band and gap structure, and despite a change from singlet- to triplet-dominant pairing, these superconducting parameters change continuously with cation substitution. Weak-coupling BCS and Ginzburg-Landau relations appear to be obeyed, suggesting that this may be a particularly uncomplicated system for studying the effect of a lack of inversion symmetry.

DOI： 10.1088/1742-6596/400/2/022096

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The spin singlet and spin triplet superconducting states can coexist in noncentrosymmetric crystal structures like Li2T3B (T: Pd, Pt), while it is prohibited in ordinary crystal structures. In this study, we focused our research on non-magnetic impurity effect in Li2T3B(T: Pd, Pt). The nature of the pair breaking by non-magnetic impurity in the parity mixing superconducting state is still unclear. We investigated the effect of non-magnetic impurity on s-wave dominant parity mixing superconductor Li2Pd3B by substituting B with Al. In this substitution process, we controlled the quality of the samples and showed their quality deteriorations through the measurement of residual resistivity at T-c. Furthermore, we checked the relations of residual resistivity and T-c as well as its superconducting phase diagram. Our results showed that s-wave dominant parity mixing superconductor Li2Pd3B exhibits the small T-c suppression attributed by the non-magnetic impurities and defects, while the H-c2 value clearly increased about 1.5 times in the poor quality samples. Such behaviours are similarly observed in ordinary s-wave superconductors.

DOI： 10.1088/1742-6596/391/1/012084

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The H-T phase diagram and several superconducting parameters for the noncentrosymmetric system Li-2(Pd1-xPtx)(3)B have been determined as a function of cation substitution x. Notably, the coherence length may be linear in platinum concentration. Despite the superconducting pairing state and band structure apparently changing fundamentally, the H-T phase diagram is essentially unchanged. Unusual aspects of the shape of the H-T phase diagram are discussed. The upper critical field H-c2(0) is not anomalously high for any Pt content, likely due to an absence of high carrier masses-in such a case, the value of H-c2(0) would not serve as a probe for novel physics.

DOI： 10.1103/PhysRevB.84.059908

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We report the B-11 NMR measurements in non-centrosymmetric superconductors Li-2(Pd1-xPtx)(3)B (x = 0.0, 0.2, 0.5, 1.0), Mg9.Ir19B16.7 and Mg10.5Ir19B17.1. In Li-2(Pd1-xPtx)(3)B, BCS superconducting state for x = 0-0.5 evolves into an exotic state with line nodes in the gap function for x = 1, which is attributed to the enhanced spin-orbit coupling due to heavy element Pt. In Mg9.3Ir19B16.7 and Mg10.5Ir19B17.1, Cooper pairs are predominantly in the spin-singlet state with an isotropic gap. However, in Mg10.5Ir19B17.1 the spin susceptibility remains finite even in the zero-temperature limit, which is due to the defects that enhance the spin-orbit coupling and bring about more spin-triplet component. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.12.029

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We report the B-11 and Pt-195 NMR measurements in non-centrosymmetric superconductors Li-2(Pd1-xPtx)(3)B (x = 0.0, 0.2, 0.5, 1.0). From the measurements of spin-lattice relaxation time (T-1), we found that there was a coherence peak (CP) just below superconducting transition temperature (T-c) for x = 0-0.5 but no CP in x = 1. We demonstrated that the system for x = 0-0.5 were BCS superconductors but there existed line node in the superconducting gap for x = 1.0. The Pt-195 Knight Shift in x = 0.2 decreased below T-c indicating spin-singlet state. The results showed that BCS superconducting state evolves into an exotic state with line-nodes in the gap function when x is increased, as the spin-orbit coupling is enhanced. (C) 2010 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2010.05.043

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We investigate on the evolution of the superconducting transition temperature upon a substitution of Pd by Pt in the noncentrosymmetric superconductor Li-2(Pd1-xPtx)(3)B. The spin singlet and spin triplet superconducting states can coexist in noncentrosymmetric crystal structures like Li2T3B (T=Pt, Pd), while it is prohibited in ordinary crystal structures. This study is conducted to investigate the crossover nature in Li-2(Pd1-xPtx)(3) B (x= 0-1) for obtaining information on the parity mixing. We have succeeded in synthesizing samples which have higher T-c than previous results around x=1. A lot of samples have been synthesized with different ratios of x, and we found that the value of T-c changed continuously and there was no clear discontinuity between spin singlet dominant (x similar to 0) and spin triplet dominant (x similar to 1) state in T-c value, although the x dependence of T-c is decreasing nonlinearly with the increase of x. The higher x region around x similar to 0.8 seems to be suppressed from linear behaviour.

DOI： 10.1088/1742-6596/200/1/012183

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.64.2.3.0_434_2

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DOI： 10.18926/15108

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Long ago S. B. Roy and co-workers had explored the appearance of anomalous paramagnetic response in the magnetization data near the H-c2 phase boundary in samples of CeRu2. Recently, an anomalous paramagnetic response has also been demonstrated in a Borocarbide superconductor LuNi2B2C, where the phenomenon has been related to the symmetry transition of the flux line lattice. We report here the magnetization data from vibrating sample magnetometer in a single crystal of CeRu2. We demonstrate that the magnetization profile is dipolar like only at very low fields and as the applied field increases it gets drastically modified. The presence of quadrupole moment along with the dipole moment is needed to justify such a magnetization profile. We report that the quadrupole moment undergoes a large modulations near the H-c2 phase boundary. Hence, there is a possibility of response from quadrupole moment getting mixed with that from dipolar response which might lead to paramagnetic anomaly prior to H-c2.

DOI： 10.1088/1742-6596/150/5/052206

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The excitation spectra with the vibronic structure near the 360 nm absorption band and emission spectra with the vibronic structure near the 430 nm emission band have been studied comparing neutron irradiated alpha-Al2O3 at pile temperature (360 K) and at 20 K. In particular the optical vibronic emission spectra of the neutron irradiated single crystal alpha-Al2O3 in low temperature have been analyzed. Huang Rhys factors of 360 nm excitation and 430 nm emission band are calculated. Also, Debye temperature has been estimated by curve fitting using temperature dependence of the excitation band. It can be seen that the excitation band derives from F-2(+) type center and emission band is suggested as F+ type center.

DOI： 10.1016/j.phpro.2009.07.040

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We present B-11 nuclear magnetic resonance (NMR) measurements in superconductors Li-2(Pd,Pt)(3)B without inversion symmetry. In Li2Pd3B, the spin lattice relaxation rate 1/T-1 shows a well-defined coherence peak below T-c, and follows an exponential temperature variation exp(-Delta/k(B)T) at low temperatures. At a magnetic field of 1.46 T, the energy gap Delta was found to be 1.1k(B)T(c), but it recovers to 1.5k(B)T(c) at a field of 0.44 T, which is quite close to the value 1.75k(B)T(c) for a weak coupling BCS superconductor. This behavior is in contrast to that found in Li2Pt3B where 1/T-1 is proportional to T-3, and the difference between the two compounds is ascribed to the different strength of spin orbit coupling.

DOI： 10.1143/JPSJS.77SA.348

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.62.2.3.0_546_4

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We performed high-resolution angle-resolved photoemission spectroscopy (ARPES) on quasi-two-dimensional rare-earth intermetallic compounds LaAgSb2 and CeAgSb2. In CeAgSb2, we found highly dispersive bands in the vicinity of the Fermi level, showing a hole-like dispersion centered at the Gamma(Z) point in the Brillouin zone. These bands produce small hole pockets at the zone center, in good agreement with the band calculation of LaAgSb2. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.101

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We have grown many kinds of high-quality single crystals of cerium and uranium compounds and studied the Fermi surface properties via the de Haas-van Alphen experiments and energy band calculations. The quasi-two-dimensional electronic states are clarified in some compounds such as USb2, CeCoIn5, UPtGa5 and most likely UIr. In a ferromagnet CeRh3B2, we have found unique electronic states with quasi-one-dimensional character.

DOI： 10.1088/0953-8984/19/12/125203

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SmCoIn5 crystallizes in the tetragonal HoCoGa5 type structure. This type of crystal structure have attracted much attention because new heavy-fermion superconductivity with very high superconducting transition temperature T-c = 18.5 K was discovered in PuCoGa5. It is expected that Sm has a similar ground state to Pu compounds. Thus we have measured the electrical resistivity on a single crystal of SmCoIn5 using a cubic anvil pressure cell at temperature 2-300 K under high pressure from 2 to 8 GPa. The value of T-N that was 11.9 K at ambient pressure in SmCoIn5 increased to 13.2 K at P = 2 GPa,. Above 2 GPa, It decreased monotonously with increasing pressure and was 12.6 K at 8 GPa. It may be thought that the 4f electrons in SmCoIn5 are more localized than 5f electrons in PuCoGa5.

DOI： 10.1143/JPSJS.76SA.62

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SmMIn5 (M = Co, Rh, Ir) crystallizes in the tetragonal HoCoGa5-type structure. This type of crystal structure is noticed as tetragonal variants of the AuCu3-structure, in which new superconductors were discovered. PuCoGa5 and PuRhGa5 are also the interesting superconductors. On the other hand, it is expected that Sm has a ground state similar to Pu compounds. We have succeeded in growing single crystals of SmMIn5 by the flux method. SmRhIn5 and SmIrIn5 showed the antiferromagnetic ordering and extra transitions below T-N, which is almost same as the results in the previous report. We have succeeded in growing single crystals of SmCoIn5. It also showed the antiferromagnetic ordering and extra transitions below T-N = 11.9 K. The temperatures of these anomalies are 6. 7.6 and 11.9 K and lowest found in SmMIn5 compounds. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.148

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Recent studies show that the non-Fermi liquid (NFL) behavior of MnSi and Fe spans over an unexpectedly broad pressure range, between the critical pressure p(c) and around 2p(c). In order to determine the extension of their NFL regions, we analyze the evolution of the resistivity rho(T)similar to A(p)T-n at higher pressures. We find that in MnSi the n = 3/2 exponent holds below 4.8 GPa approximate to 3p(c), but it increases above that pressure. At 7.2 GPa we observe the low-temperature Fermi liquid exponent n = 2 whereas for T > 1.5 K, n =5/2. Our measurements in Fe show that the NFL behavior rho similar to T-5/3 extends at least up to 30.5 GPa, above the entire superconducting (SC) region. In the studied pressure range, the onset of the SC transition reduces by a factor 10 down to T-c(onset)(30.5 GPa) = 0.23 K, while the A-coefficient diminishes monotonically by around 50%. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.062

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CeAgSb2 crystallizes in the tetragonal ZrCuSi2 type structure (P4/nmm), which consists of Sb-Ce, Sb-Ag-Ce, Sb-Sb layers. It shows the peculiar anisotropic ferromagnetic ordering below 9.7 K with a small ordered moment of 0.33 mu B. Its residual resistivity steeply increases above p(c) congruent to 3.3 GPa where the magnetic order disappears. It is expected that the p-f mixing on the peculiar hollow square pillar-like Fermi surface plays an important role in CeAgSb2, while similar Fermi surfaces were not observed in LaAgSb,. We have measured the anisotropy in the electrical resistivity of CexLa1-xAgSb2 to study the p-f mixing effect. Small humps were observed in the temperature dependence of the resistivity in (CeLa1-xAgSb2)-La-x. We expected them the CDW transition. The CDW state coexisted with the ferromagnetic state around x = 0.2. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.305

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X-ray absorption magnetic circular dichroism (XMCD) at the U N-4.5 edges was measured for the ferromagnetic superconductor UGe2 in the normal state. The orbital and spin magneic moments deduced from the sum rule analysis of the XMCD data indicate that the U atom in UGe2 is considered to be closer to the trivalent state rather than the tetravalent state. The temperature dependence of the XMCD signal does not show any significant anomaly at T-* similar to 30K, where the resistivity anomaly was observed at ambient pressure. The XMCD measurement at the U N-2,N-3 edge indicates that the U 6d electrons have negligibly small magnetic contributions.

DOI： 10.1143/JPSJ.75.024704

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

We report a B-11 NMR measurement on the recently discovered superconductor Li2Pd3B. The nuclear spin lattice relaxation rate 1/T-1 shows a well-defined coherence peak just below T-c(H=1.46 T)=5.7 K, and the spin susceptibility measured by the Knight shift also decreases below T-c. These results indicate that the superconductivity is of conventional nature, with an isotropic gap. Our results also suggest that the p-electrons of boron and the d-electrons of palladium that hybridize with boron p-electrons are primarily responsible for the superconductivity.

DOI： 10.1103/PhysRevB.71.220505

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We have performed X-ray magnetic circular dichroism (XMCD) experiments at Ge K-edge in 5f ferromagnetic superconductor UGe2(T-C = 52 K). Ge K-edge XMCD spectrum (1s -> 4p) of UGe2 reflects the magnetic response of the conduction electron states. The Ge K-edge XMCD spectrum shows a main negative peak near the edge and a small positive one at 7 eV above the edge. The amplitude of this spectrum is very large in spite of being at ligand sites. The strong spin-orbit interaction at the uranium site plays an important role in this phenomenon. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.01.415

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We report the de Haas-van Alphen (dHvA) effect and magnetoresistance in the filled-skutterudite superconductor LaRu4P12, which is a reference material of PrRu4P12 that exhibits a metal-insulator (M-I) transition at T-MI similar or equal to 60 K. The observed dHvA branches for the main Fermi surface (FS) are well explained by the band-structure calculation, using the full potential linearized augmented-plane-wave method with the local-density approximation, suggesting a nesting instability with q=(1,0,0) in the main multiply connected FS as expected also in PrRu4P12. Observed cyclotron effective masses of (2.6-11.8)m(0), which are roughly twice the calculated masses, indicate the large mass enhancement even in the La-skutterudites. Comparing the FS between LaRu4P12 and PrRu4P12, an essential role of c-f hybridization cooperating with the FS nesting in driving the M-I transition in PrRu4P12 is clarified.

DOI： 10.1103/PhysRevB.71.132502

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We report the de Haas-van Alphen (dHvA) effect and magnetoresistance in the filled-skutterudite superconductor LaRu4 P12, which is a reference material of PrRu4 P12 that exhibits a metal-insulator (M-I) transition at TMI 60 K. The observed dHvA branches for the main Fermi surface (FS) are well explained by the band-structure calculation, using the full potential linearized augmented-plane-wave method with the local-density approximation, suggesting a nesting instability with q= (1,0,0) in the main multiply connected FS as expected also in PrRu4 P12. Observed cyclotron effective masses of (2.6-11.8) m0, which are roughly twice the calculated masses, indicate the large mass enhancement even in the La-skutterudites. Comparing the FS between LaRu4 P12 and PrRu4 P12, an essential role of c-f hybridization cooperating with the FS nesting in driving the M-I transition in PrRu4 P12 is clarified. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.132502

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We report high-resolution angle-resolved photoemission spectroscopy of LaRh3B2, which is a nonmagnetic reference compound of RRh3B2 (R: rare-earth metals). We found two hole-like Fermi surfaces (FSs) and two electron-like FSs centered at Gamma(A) and K(H) points, respectively. The estimated volume of FSs at Gamma(A) point shows a good agreement with the LDA band calculation, while the band dispersion and the topology of FSs at K(H) point show a remarkable disagreement. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.06.023

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We have studied de Hass van Alphen (dHvA) effect under pressure for a pressure-induced superconductor CeRhIn5 and a superconductor CeCoIn5. The topology of the Fermi surface in CeRhIn5 and CeCoIn5 are found to be unchanged up to 2.1 GPa and 3.1 GPa, respectively. On the other hand, the effective mass of CeRhIn5(CeCoIn5) decreases (increases) remarkably with increasing pressure. (C) 2003 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2003.11.087

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Thermal expansion and magnetostriction measurements have been performed on a single crystal CeRh3B2 with an unusually high Curie temperature T-C similar to 120 K: The thermal expansion coefficients show a weak anomaly at T-C and characteristic positive and negative peaks around 150 K for [0001] and [10(1) over bar 0], respectively. The magnetostriction at 4.2 K for the field along the basal plane is very small, with an order of 10(-5); suggesting a localized nature of Ce - 4f moments. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.12.1307

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We searched for an experimental condition of crystal growth for a ferromagnetic superconductors of UGe2 and URhGe. Samples were prepared for both polycrystalline and single crystals, which were arc-melted and grown by the Czochralski-pulling method in a tetra-arc furnace, respectively. Annealing is an important process to enhance sample-quality, namely the residual resistivity ratio. We tried to anneal the samples under various temperatures, which were wrapped by the Ta-foil and vacuum-sealed in the quartz ample, together with the solid state electrotransport method in ultra-high vacuum. The highest residual resistivity ratio was 900 for UGe2 and 41 for URhGe. (C) 2003 Published by Elsevier B.V.

DOI： 10.1016/j.jmmm.2003.12.1083

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We report further resistive measurements under pressure of samples of iron from multiple sources. The normal state resistivity of E-iron varied as rho(0) + AT(5/3) at low temperature over the entire superconducting pressure domain. The superconductivity could be destroyed by mechanical work, and was restored by annealing, demonstrating sensitivity to the residual resistivity rho(0). There is a strong correlation between the rho(0) and A coefficients and the superconducting critical temperature T-c. The critical field B-c2 corresponding to the maximum Tc was found to be 0.73 T, implying a coherence length of about 20 nm, i.e. slightly shorter than the electronic mean free path. Within the partial resistive transition there was a significant current dependence, with V (I) = a (I - I-0) + bI(2), and a much greater than b, possibly indicating flux-flow resistivity, even in the absence of an externally applied magnetic field.

DOI： 10.1088/0953-8984/16/14/021

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We have measured the electrical resistivity, magnetic Susceptibility, high-field magnetization, specific heat and de Haas-van Alphen (dHvA) oscillation of Ce(2)Rhln(8), together with the dHvA oscillation of La2RhIn8. In La2RhIn8 we detected three kinds of dHvA branches showing cylindrical Fermi surfaces, which are well explained by the result Of FLAPW energy band calculations. The corresponding two dHvA branches were detected in Ce2RhIn8, indicating that the topology of the Fermi surface in Ce2RhIn8 is approximately the same as that of LaRhIn8. The magnetic susceptibility and magnetization of Ce2RhIn8 were analyzed on the basis of the crystalline electric field scheme of localized-4f energy levels. Pressure-induced superconductivity was confirmed above 1.2GPa from the resistivity and ac-susceptibility measurements.

DOI： 10.1143/JPSJ.73.649

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The CeIrIn5-Ag junctions of about 2x10(-9) cm(-2) area have been made using microfabrication techniques, and the surface superconducting state of CeIrIn5, which has two characteristic temperatures T-0 and T-c, has been investigated, where T-0 and T-c are the transition temperature to zero-resistivity state and the bulk, thermodynamic transition temperature, respectively. The temperature, below which superconducting anomalies are observed, varies from junction to junction, and yet it is always well above T-c=0.4 K. This result, together with no indication of transition at T-c, suggests that at least the surface of CeIrIn5 is in the superconducting state above T-c. The data on the critical current I-c in superconducting anomalies point to the possibility to define a local transition temperature for each junction.

DOI： 10.1023/A:1026083124132

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We have carried out de Haas-van Alphen (dHvA) experiments on a ferromagnet CeRh3B2 with an extremely high Curie temperature T-C similar or equal to 120 K and a non-4f reference compound LaRh3B2. The dHvA data of LaRh3B2 are well explained by the results of energy band calculations. The topology of the Fermi surfaces in CeRh3B2 is found to be very similar to that of LaRh3B2, possessing wavy but flat Fermi surfaces in the basal plane. Observation of a quasi-one-dimensional electronic state is the first such case in a rare earth compound.

DOI： 10.1088/0953-8984/15/46/L02

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

DOI： 10.1143/JPSJ.72.2692

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

In order to understand the anisotropic magnetic and electrical properties of ternary compounds CeTSb2 (T=Cu, Au, Ni) with the tetragonal structure, we have grown single crystals of this series by the self-flux method and measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat. CeCuSb2 and CeAuSb2 are found to order antiferromagnetically with Neel temperatures of 6.9 K and 5.0 K, respectively, while CeNiSb2 is a ferromagnet with a Curie temperature of 6.0 K with an easy axis of magnetization oriented along the [100] direction. The magnetic property of CeCuSb2 shows a very small anisotropy, whereas the electrical resistivity is highly anisotropic between Jparallel to [100] and [001]. In contrast, CeAuSb2 and CeNiSb2 show a strong anisotropy both in the magnetic and electrical measurements, although the magnetic easy axis is interchanged with respect to each other. The anisotropy in the magnetic properties has been explained on the basis of a crystalline electric-field model.

DOI： 10.1103/PhysRevB.68.054427

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We carried out a de Haas-van Alphen (dHvA) experiment under pressure on a heavy-fermion superconductor, URu2Si2. The dHvA frequency, which corresponds to a nearly spherical Fermi surface, increases slightly with increasing pressure, while the corresponding cyclotron mass decreases considerably. Neither the dHvA frequency nor the cyclotron mass exhibit any abrupt change at the critical pressure of 1.5 GPa. The present result is thus inconsistent with a recent phase-separation proposal.

DOI： 10.1088/0953-8984/15/28/316

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CeRh(3)B(2) is a ferromagnet with an unexpectedly high Curie temperature and low saturation magnetic moments. The origin of its unusual magnetic behaviour remains unelucidated despite various investigations performed in the last two decades. Here we present magnetic results obtained on high-quality single crystals over a wide temperature range. Some new magnetic features are uncovered and possible approaches to explaining its magnetism are briefly discussed.

DOI： 10.1088/0953-8984/15/28/349

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Ce unoccupied 5d electronic states of the nonmagnetic heavy-fermion compound CeRu2Si2 have been investigated by means of x-ray magnetic circular dichroism (XMCD) experiments. We measure the magnetic field dependences of the Ce L-2,L-3-edge XMCD of a powder sample with a transmission mode at about 2 K. The magnetic field dependence of the L-2-edge x-ray absorption spectrum shows a slight enhancement of the white line with metamagnetic behaviour, indicating reduction of the c-f hybridization. The L-2 XMCD spectrum shows a single positive lobe, while the L-3 XMCD spectrum consists of a main negative peak and two small negative satellite peaks. The main structure of CeRu2Si2 is similar to that of CeRu2Ge2.

DOI： 10.1088/0953-8984/15/28/345

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The exotic features of the Pr-based filled skutterudites are reviewed based on the electronic transport properties, specific heat and de Haas-van Alphen experiments, putting the emphasis on PrFe4P12 and PrOs4Sb12. As references, the experiments on the related La- and Ce-filled skutterudites are also examined and discussed. Compared to their La reference compounds, the Fermi surface is very similar in PrOs4Sb12, suggesting the well localized character of 4f electrons, while it looks largely different in PrFe4P12. For the cyclotron effective mass, both PrFe4P12 and PrOS4Sb12 exhibit a strong enhancement, in reasonable agreement with the large specific heat coefficient.

DOI： 10.1088/0953-8984/15/28/326

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We have grown single crystals of U2FeGa8 and U2RhGa8 with the tetragonal structure by the self-flux method. Both compounds are Pauli paramagnets and possess relatively large gamma-values of 52 and 43 mJ K-2/mol U, respectively.

DOI： 10.1088/0953-8984/15/28/317

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The spin-polarized electron momentum distribution (magnetic Compton profile: MCP) of ferromagnetic CeRh3B2 has been measured using the magnetic Compton scattering technique at 10 K for the [1120] direction. In this compound, the orbital moment dominates the magnetization. An analysis of the MCP reveals that the Ce 4f and Ce 5d spin moments are aligned parallel with a value of -0.68 +/- 0.08 and 0.41 +/- 0.04 mu(B), respectively, while Rh 4d electrons do not carry any significant spin moment. The ratio of orbital to spin moments for Ce 4f electrons, which has been determined from comparison of the present data with recent polarized neutron diffraction data, is rather smaller than that for Ce3+ ions. This result implies strong hybridization of the Cc 4f orbital with the orbitals on the surrounding ions.

DOI： 10.1088/0953-8984/15/28/348

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We have measured the electrical resistivity under pressure up to 2 GPa for an antiferromagnet, CeRhGe. The resistivity at ambient pressure decreases monotonically below a Neel temperature T-N = 10 K. With increasing pressure P, the resistivity has a peak around 10 K, which is anomalously enhanced up to 1.2 GPa. With further increasing pressure, the resistivity peak is diminished; the Neel temperature becomes zero at a critical pressure P-c = 9 GPa. The A-value of the resistivity rho in the Fermi liquid relation rho = rho(0) +AT(2) is also found to increase with increasing pressure and has a maximum at Pc which corresponds to the value for the heavy-fermion superconductor CeCu2Si2.

DOI： 10.1088/0953-8984/15/29/102

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We present descriptions of the single crystal growth of uranium and cerium compounds via the Czochralski-pulling, self-flux and vapour transport methods. We also report the results of de Haas-van Alphen experiments and energy band calculations for a Hill-plot rule of UX3 (X: Si, Ge, Sn and Pb), heavy fermion systems of UPt3 and UPd2Al3, quasi-two-dimensional electronic states of UPtGa5, UX2 (X: Bi, Sb, As, P) and CeCoIn5, characteristic semimetals of UC and CeAgSb2, and quantum critical phenomena in UGe2 and CeRh2Si2.

DOI： 10.1088/0953-8984/15/28/301

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

When pressure is applied to cerium and uranium compounds, the magnetic ordering temperature is suppressed and becomes zero at a critical pressure P-c. Around P-c, non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via a de Haas-van Alphen (dHvA) experiment when pressure crosses P-c. The dHvA experiment under pressure was done for the antiferromagnets CeRh2Si2 and CeRhIn5, and for a ferromagnet UGe2. We found an abrupt change of the Fermi surface for CeRh2Si2 and UGe2 when crossing P-c, indicating a first-order like phase transition. For CeRhIn5, the topology of the Fermi surface was unchanged, but the cyclotron mass increased steeply above 1.6 Gpa, where superconductivity sets in. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(03)00070-2

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We carried out the de Haas-van Alphen experiment under pressure for a heavy fermion antiferromagnet URu2Si2. The detected cyclotron mass for a nearly spherical Fermi surface under pressure changes considerably, reflecting a change of the magnetic moment. The present result is, however, inconsistent with the recent phase separated proposal. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02443-2

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The Josephson effect between a single crystal CeTIn5 (T = Co, Ir) and an s-wave superconductor has been investigated for CeTIn5-Cu-Nb junctions. Josephson critical current I-c is observed just below superconducting transition temperature T-c for CeCoIn5, while the temperature below which I-c appears varies from junction to junction and I-c rises gradually at first for CeIrIn5, probably reflecting a distribution of the local transition temperature in CeIrIn5, (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02734-X

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We have studied the de Haas-van Alphen (dHvA) effect under pressure for an antiferromagnet CeRhIn5, where the antiferromagnetic state is changed into the superconducting state at higher pressures than 1.6 GPa. It is clarified from the present dHvA experiment that the topology of the Fermi surface is unchanged up to 2.1 GPa but the cyclotron mass increases strongly above 1.6 GPa. Superconductivity is found to be realized in this heavy fermion state. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02366-9

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We succeeded in growing high-quality single crystals of UTGa5 (T: Fe, Co and Pt) by the self-flux method, and measured the de Haas-van Alphen effect. With increasing the number of 3d-electrons, from Fe to Pt, the Fermi surface is found to change systematically, indicating cylindrical Fermi surfaces in UFeGa5 and UPtGa5. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02496-1

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CeRh3B2 has the highest Curie temperature of 120 K in the cerium compounds, with a saturation moment of about 0.4mu(B)/Ce. We have succeeded in growing high-quality single crystals of CeRh3B2, and measured the de Haas-van Alphen (dHvA) effect and the transverse magnetoresistance to clarify the 4f-electronic state. The dHvA frequencies are found to be in the range from 0.4-2 kT with the cyclotron mass of 1.7-2.4m(0). The magnetoresistance suggests the existence of open orbits on the Fermi surface. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02482-1

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We report the first successful observation of the de Haas van Alphen effect in the filled skutterudite LaRu4P12. Observed Fermi surfaces (FSs) are close to those expected from the band calculation. The effective mass m(c)* is roughly twice compared to the calculated band mass. Assuming the similarity of FS between LaRu4P12 and PrRu4P12, the FS nesting with q = (1, 0, 0) as a possible origin of the M-I transition in PrRu4R12 is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)01811-2

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We have succeeded in growing single crystals of the cerium-transition metal intermetallics CeTSb2 (T: Cu, An, Ni) with the tetragonal structure via the self-flux method, and measured the electrical resistivity, magnetic, susceptibility, magnetization and specific heat. CeCuSb2 and CeAuSb2 are antiferromagnets with Neel temperatures of 6.9 and 5.0 K, respectively. CeCuSb2 is a heavy-fermion antiferromagnet with an electronic specific heat coefficient gamma = 200 mJ/K-2 Mol. CeAuSb2 also is a similar compound with an antiferromagnetic easy axis along the [001] direction. CeNiSb2 is a ferromagnet with a Curie temperature of 6.0 K. The easy axis is oriented along [100], with a moment of 0.6mu(B)/Ce. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)01747-7

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We have carried out the de Haas-van Alphen (dHvA) experiment to clarify the Fermi surface property of an antiferromagnet UPtGa5. and have constructed the magnetic phase diagram from the high-field magnetization measurement. From the dHvA experiment. the Fermi surface is found to consist of four kinds of nearly cylindrical Fermi surfaces along the tetragonal 1001] direction. which are approximately explained by the result of the spin-polarized energy band calculations based on the antiferromagnetic structure with a sequence of (up arrowdown arrow) along [001]. Relatively large cyclotron masses are detected for carriers of the corresponding Fermi surfaces, ranging from 10 to 24 m(o) (m(o): rest mass of an electron). 5f electrons are thus concluded to be itinerant and also to contribute to the magnetic moment at the uranium sites.

DOI： 10.1143/JPSJ.72.576

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We have studied the effect of pressure on the electrical resistivity of a high-quality single crystal CeAgSb2 which has a small net ferromagnetic moment of 0.4 mu(B)/Ce. The magnetic ordering temperature. T-ord = 9.7 K decreases with increasing pressure p and disappears at a critical pressure p(c) similar or equal to 3.3 GPa. The residual resistivity, which is close to zero up to 3 GPa, increases steeply above 3 GPa, reaching 55 muOmega cm at p(c). A huge residual resistivity is found to appear when the magnetic order disappears.

DOI： 10.1088/0953-8984/15/4/101

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAGIELLONIAN UNIV PRESS  

When pressure is applied to the cerium and uranium compounds, their magnetic ordering temperatures are suppressed and become zero at a critical pressure P-c. Around P-c non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via the de Haas-van Alphen (dHvA) experiment when pressure crosses P-c. The dHvA experiment under pressure was done for antiferromagnets CeRh2Si2, CeRhIn5 and URu2Si2, and a ferromagnet UGe2. We find an abrupt change of the Fermi surface for CeRh2Si2 and UGe2 when crossing P-c, indicating a first-order like phase transition. For CeRhIn5 and URu2Si2, a change of the cyclotron mass is clearly observed.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS  

We have succeeded in growing high-quality single crystals of CeAgSb2, and carried out the de Haas-van Alphen (dHvA) experiment. Cylindrical Fermi surfaces were observed, together with closed Fermi suraces. The effective cyclotron mass is in the range from 0.9 to 32m(0). Large cylindrical Fermi surfaces occupying half of the Brillouin zone were detected, which are highly different from small Fermi surfaces in the reference compounds LaAgSb2 and YAgSb2 with a semimetalic character. CeAgSb2 is the first example in which the 4f electron becomes itinerant and possesses the magnetic moment.

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We searched for an experimental condition of crystal growth for a ferromagnetic superconductor URhGe. Samples were prepared for both poly-crystalline and single crystals, which were arc-melted and grown by the Czochralski-pulling method in a tetra-arc furnace, respectively. Annealing is an important process in order to increase sample-quality, namely the residual resistivity ratio. We tried to anneal the samples under various temperatures, which were wrapped by the Ta-foil and vacuum-sealed in the quartz ample, together with the solid state electrotransport (SSE) method in ultra-high vacuum.

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We have succeeded in observing the de Haas-van Alphen (dHvA) effect in PrOS4Sb12. The Fermi surface topology is similar to the reference compound LaOS4Sb12, indicating the localized character of 4f-electrons. The cyclotron effective mass, enhanced by about four times compared with LaOs4Sb12, is a direct evidence of the strong electron correlation in this compound.

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We have investigated the de Haas-van Alphen effect in the Pr-based heavy-fermion superconductor PrOs4Sb12. The topology of Fermi surface is close to the reference compound LaOs4Sb12 and well explained by the band-structure calculation based on the FLAPW (full potential linearized augmented-plane-wave)-LDA (local-density approximation) + U method, where the 4f electrons are localized. We have confirmed a highly enhanced cyclotron effective mass (2.4-7.6)m0, which is apparently large compared to the usual Pr-based compounds.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：TAYLOR & FRANCIS LTD  

We have carried out the de Haas-van Alphen (dHvA) experiment, together with electrical resistivity, magnetic susceptibility, magnetization and specific heat experiments on a high-quality single-crystal CcAgSb(2), which has a small net ferromagnetic moment of 0.4 mu(B) per Cc atom. The bulk magnetic properties are well explained by the crystalline electric field scheme. On the other hand, large dHvA frequencies of 10(8) Oe, which correspond to cylindrical Fermi surfaces, were detected by the dHvA measurement for the magnetic field along the tetragonal [001] direction, indicating the quasi-two-dimensional electronic structure. The dHvA branches of CeAgSb2 are highly different from those with small dHvA frequencies of 10(7) Oe for the reference compounds LaAgSb2 and YAgSb2 which exhibit a semimetallic character. The dHvA results have been compared with the results of the energy band calculations. It was concluded that the 4f electron is mainly localized and that the Fermi surface of CeAgSb2 is similar to that of LaAgSb2, but it is slightly enlarged so as to form the large orbits along a hollow cylindrical Fermi surface.

DOI： 10.1080/1364281021000036823

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Evolution of the pressure-induced heavy fermion state and superconductivity in CeRhIn5 have been established by high-pressure Fermi surface studies using dHvA technique. The effective mass of the conduction electrons named branch beta(2) increases from 5.5 m(0) at ambient pressure to 20 m(0) at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 m(0) at 2.1 GPa, with a concomitant increase of the superconducting transition temperature. However, the underlying Fermi surface remains approximately same even at 2.1 GPa, strongly suggesting that antiferromagnetic fluctuations of Ce moments do not contribute to the volume of the Fermi surface, but enhance the cyclotron mass of the conduction electrons.

DOI： 10.1103/PhysRevB.66.214510

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We have investigated the de Haas-van Alphen effect in the Pr-based heavy-fermion superconductor PrOs4Sb12. The topology of Fermi surface is close to the reference compound LaOs4Sb12 and well explained by the band-structure calculation based on the FLAPW (full potential linearized augmented-plane-wave)-LDA (local-density approximation) +U method, where the 4f electrons are localized. We have confirmed a highly enhanced cyclotron effective mass (2.4-7.6)m(0), which is apparently large compared to the usual Pr-based compounds.

DOI： 10.1103/PhysRevB.66.220504

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We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite PrFe4P12 exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass mc* = 81 m0 in the high field phase, which indicates that PrFe4P12 is the first Pr compound in which really heavy mass has been unambiguously confirmed. Also in the low field nonmagnetic ordered phase (LOP), we observed the dHvA branch with mc* = 10 m0 that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite PrFe4P12 exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass m(c)(*)=81 m(0) in the high field phase, which indicates that PrFe4P12 is the first Pr compound in which really heavy mass has been unambiguously confirmed. Also in the low field nonmagnetic ordered phase (LOP), we observed the dHvA branch with m(c)(*)=10 m(0) that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation.

DOI： 10.1103/PhysRevB.66.134411

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

Last year. iron was reported. to become superconducting at temperatures., below 2 K and pressures between 15 and 30 GPa, Nature 412 (2001) 316. The evidence presented was a weak resistivity drop, suppressed by a magnetic field above 0.2 T. and a small Meissner Signal. However, a compelling demonstration, such as the occurrence of zero resistance, was lacking. Here we report the measurement of a complete resistive transition at 22.2 GPa with an onset slightly above 2 K in two very pure samples of iron, of different origins. The superconductivity appears unusually sensitive to disorder, developing only when (lie electronic mean free path is above a threshold value, while the normal state resistivity is characteristic of a nearly ferromagnetic metal. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0375-9601(02)00725-9

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We have studied the effect of pressure on the electrical resistivity of the antiferrornagnet CeMg2Cu9 which crystallizes in the hexagonal structure. The structure is built up of alternating MgCu2 Laves-type and CeCu5-type layers along the [0001] direction. The Neel temperature T-N = 2.7 K at ambient pressure decreases with increasing pressure p and disappears at a critical pressure p(e) similar or equal to 2.5 GPa. Correspondingly, the residual resistivity rho(0) and the coefficient A in a Fermi-liquid relation rho = rho(0) + AT(2) are found to have maximum values around p(e).

DOI： 10.1088/0953-8984/14/14/101

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

We observed de Haas-van Alphen (dHvA) oscillations in CeRh2Si2 at 1.3 GPa, higher than the quantum critical pressure p(c)similar or equal to1.0 GPa. Three observed dHvA branches correspond to the result of the 4f-itinerant model. Their cyclotron masses are large, being 24m(0), 29m(0) and 31m(0), about 4 times larger than the corresponding band masses. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01359-X

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The angular dependence of de Haas-van Alphen effect has been measured to reveal the electronic structure of filled skutterudite PrRu4Sb12. The angular dependence of de Haas-van Alphen frequency of PrRu4Sb12 is in good agreement with that of LaRu4Sb12. Compared with PrFe(4)Pi(12), no anomalous enhancement of cyclotron effective mass has been observed in this system. This change of electronic structure is attributed to the difference in the c - f hybridization strength, which is expected from the large difference in the lattice parameters. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01260-1

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We have succeeded in growing a high-quality single crystal of UIr with the monoclinic structure by the Czochralski pulling method in a tetra-arc furnace. UIr is a ferromagnetic compound. Its Curie temperature TC is 46K and the magnetic moment is found to be oriented along the [1 0 1̄] direction by the magnetization measurement. The magnetic moment is 0.5 μB/U. We have observed the de Haas-van Alphen oscillation. All the detected branches have heavy cyclotron effective masses ranging from 9.6 to 32 m0. They are consistent with the electronic specific heat coefficient γ = 48.5 mJ/K2 mol. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01331-X

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We report the de Haas-van Alphen (dHvA) experiment on the filled skutterudite (formula presented) exhibiting apparent Kondo-like behaviors in the transport and thermal properties. We have found enormously enhanced cyclotron effective mass (formula presented) in the high field phase, which indicates that (formula presented) is the first Pr compound in which really heavy mass has been unambiguously confirmed. Also in the low field nonmagnetic ordered phase (LOP), we observed the dHvA branch with (formula presented) that is quite heavy taking into account its small Fermi surface volume (0.15% of the Brillouin zone size). The insensitivity of mass in LOP against the magnetic field suggests that the quadrupolar interaction plays a main role both in the mass renormalization and the LOP formation. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.134411

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

We have studied Fermi surface properties of LaRhIn5 and CeTIn5 (T: Co, Rh and Ir) via the de Haas-van Alphen (dlivA) experiment. These Fermi surfaces are nearly cylindrhnal, reflecting the unique tetragonal crystal structure. The cyclotron mass or the gamma value is found to be strongly field-dependent in CeCoIn5. We have also carried out the dIlvA experiment under pressure for CeRhIn5.

DOI： 10.1143/JPSJS.71S.276

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We have studied Fermi surface properties of LaRhIn5 and CeTIa(5) (T: Co, Rh and Ir) via the de Haasvan Alphen (dHvA) experiment. The Fermi surface of a non-4f reference compound LaRhIn5 is quasi-two dimensional, reflecting the unique tetragonal crystal structure, which is consistent with the result of FLAWP energy band calculations. The Fermi surface of an antiferromagnet CeRhIn5 is similar to that of LaRhIn5 although the cyclotron mass in CeRhIn5 is roughly by one order larger than that in LaRhIn5. Both Fermi surfaces are. however, different from those of CeCoIn5 and CcIrIn(5) which are well explained by the 4f-itinerant band model. The 4f electrons in CeRhIn5 thus do not contribute to the volume of ate Fermi surface. We have also studied magnetic and superconducting properties of CeCoIn5 and CeIrIn5.

DOI： 10.1143/JPSJ.71.162

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Evolution of the pressure-induced heavy fermion state and superconductivity in (formula presented) have been established by high-pressure Fermi surface studies using dHvA technique. The effective mass of the conduction electrons named branch (formula presented) increases from 5.5 (formula presented) at ambient pressure to 20 (formula presented) at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 (formula presented) at 2.1 GPa, with a concomitant increase of the superconducting transition temperature. However, the underlying Fermi surface remains approximately same even at 2.1 GPa, strongly suggesting that antiferromagnetic fluctuations of Ce moments do not contribute to the volume of the Fermi surface, but enhance the cyclotron mass of the conduction electrons. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.214510

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We have carried out the de Haas-van Alphen (dHvA) experiment, together with electrical resistivity, magnetic susceptibility, magnetization and specific heat experiments on a high-quality single-crystal CeAgSb2, which has a small net ferromagnetic moment of 0.4 μB per Ce atom. The bulk magnetic properties are well explained by the crystalline electric field scheme. On the other hand, large dHvA frequencies of 108 Oe, which correspond to cylindrical Fermi surfaces, were detected by the dHvA measurement for the magnetic field along the tetragonal [001] direction, indicating the quasi-two-dimensional electronic structure. The dHvA branches of CeAgSb2 are highly different from those with small dHvA frequencies of 107 Oe for the reference compounds LaAgSb2 and YAgSb2 which exhibit a semimetallic character. The dHvA results have been compared with the results of the energy band calculations. It was concluded that the 4f electron is mainly localized and that the Fermi surface of CeAgSb2 is similar to that of LaAgSb2, but it is slightly enlarged so as to form the large orbits along a hollow cylindrical Fermi surface. © 2002 Taylor and Francis Group, LLC.

DOI： 10.1080/13642810208222948

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Fermi surface properties of various uranium-based intermetallic compounds, including a 5f-localized compound, Pauli paramagnets, heavy fermions, antiferromagnets and ferromagnets, have been investigated by means of the de Haas-van Alphen effect. For this purpose we have grown high-quality single crystals using a purified uranium metal. Both the topology of the Fermi surface and the cyclotron mass in Pauli paramagnets such as USi3 are well explained by the band calculations. Surprisingly, the topology of the Fermi surface in heavy fermions such as UPt3 and UPd2Al3 also agree with the theoretical calculations, except for their unusually large mass enhancement. We have also succeeded in detecting a dHvA oscillation in the superconducting mixed state in the heavy fermion superconductor, UPd2Al3. Spin-polarized band calculatioins are approximately applicable to some magnetically ordered compounds such as UBi2 and UNiGa5. © 2014 Taylor and Francis Group, LLC.

DOI： 10.1080/00223131.2002.10875408

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We have investigated the de Haas-van Alphen effect in the Pr-based heavy-fermion superconductor (formula presented) The topology of Fermi surface is close to the reference compound (formula presented) and well explained by the band-structure calculation based on the FLAPW (full potential linearized augmented-plane-wave)-LDA (local-density approximation) (formula presented) method, where the (formula presented) electrons are localized. We have confirmed a highly enhanced cyclotron effective mass (formula presented) which is apparently large compared to the usual Pr-based compounds. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.220504

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We measured the magnetic susceptibilityand de Haas-van Alphen (dHvA) oscillation in UGa3 and UTGa5 (T: Fe, Ni andPt). The susceptibility in UGa3 and UTGa5 is almost temperature-independent. It does not follow the Curie-Weiss law in the paramagnetic region, being dominated by a Pauli-like contribution, although UGa3 and UTGa5 (T: Ni and Pt) order antiferro-magnetically. The electronic state in UTGa5 is unique, indicating quasi-two dimensionality. Nearly cylindrical Fermi surfaces are formed by itinerant-5f electrons. © 2014 Taylor and Francis Group, LLC.

DOI： 10.1080/00223131.2002.10875421

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The transport properties of the itinerant ferromagnet U3P4 have been studied at high pressures up to 6.0 GPa using a diamond anvil cell. The Curie temperature TC decreases with increasing pressure, but then TC cannot be assigned above 4.0 GPa. The coefficient A, assuming the Fermi liquid behavior (p(T) = p0 + AT2) at low temperatures, shows a maximum at 5.3 GPa. The temperature dependence of the resistivity at 5.0 GPa follows T 5/3 which is expected in the SCR theory of a three dimensional ferromagnet. From these results, it is concluded that the ferromagnetic-nonmagnetic transition exists at around 5.0 GPa. © 2002 Atomic Energy Society of Japan. All rights reserved.

DOI： 10.1080/00223131.2002.10875441

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The Josephson effect for a heavy-fermion superconductor CeIrIn5, which has two characteristic temperatures T-0 and T-c, has been investigated for CeIrIn5-Cu-Nb junctions, where T-0 and T-c are the temperature of the transition to the zero-resistivity state and the bulk, thermodynamic transition temperature, respectively. For all the junctions fabricated on the (110) and (001) planes of CeIrIn5, the temperature below which the Josephson effect is observed is near T-0 = 0.8 K and much higher than T-c = 0.3 K. This result suggests that at least the surface of CeIrIn5 is in a superconducting state below T-0, in which phase coherence between CeIrIn5 and Nb is possible.

DOI： 10.1088/0953-8984/13/42/102

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We present the quasi-two dimensional Fermi surface studies in rare earth and uranium compounds such as UX2 (X: Bi, Sb, As and P) and RTIn5 (R: rare earth, T: Co, Rh and Ir), together with UTGa5. The present quasi-two dimensionality is closely related to the magnetic unit cell and/or the unique crystal structure elongated along the tetragonal [001] direction, which bring about a flat Brillouin zone and produce cylindrical but highly corrugated Fermi surfaces along [001].

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The superconducting gap in a CeRu2 single crystal is investigated by point contacts. BCS-like behavior of the gap Delta in the temperature range below T-c* (T-c*<T-c, where T-c is the critical temperature) is established, indicating the presence of a gapless superconductivity region (between T-c* and T-c). The pair-breaking effect of paramagnetic impurities, supposedly Ce ions, is taken into consideration using the Scalski-Betbeder-Matibet-Weiss approach based on Abrikosov-Gorkov theory. It allows us to recalculate the superconducting order parameter Delta (alpha) (in the presence of paramagnetic impurities) and the gap Delta (p) (in the pure case) for the single crystal and for the previously studied polycrystalline CeRu2. The value 2 Delta (p)(0) approximate to 2 meV, with 2 Delta (p)(0)/k(B)T(c) approximate to 3.75, is found in both cases, indicating that CeRu2 is a "moderate" strong-coupling superconductor. (C) 2001 American Institute of Physics.

DOI： 10.1063/1.1399197

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We measured the electrical resistivity, specific heat, magnetostriction, magnetization and de Haas-van Alphen (dHvA) oscillation in UPd3 with the hexagonal structure in order to clarify the quadrupolar and magnetic properties as well as the nature of conduction electrons. The high-field magnetization measurement at 4.2 K in magnetic fields up to about 50 T reveals two-successive metamagnetic transitions at 10.2 and 17.9T for the field along the [0001] direction, and one transition at 27.6T along [1120]. From the results of magnetization as well as the magnetostriction measurements at various temperatures, we determined the magnetic phase diagram. Phase boundaries are discussed on the basis of the crystalline electric field scheme of the 5f(2) configuration and the quadrupolar interaction of O-ZX. Reflecting title localized 5f-electrons, the conduction electrons have small cyclotron effective masses ranging from 0.24 to 3.62m(0), which were determined by the dHvA experiment. The dHvA data are compared to the result of band calculations based on the 5f(2)-localized band model.

DOI： 10.1143/JPSJ.70.1731

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We present magnetization data on a weakly pinned single crystal of CeRu2 showing the existence of a stable state of the vortex matter in the peak effect (PE) region. The stable state is achieved by cycling the magnetic field by a small amplitude. It is characterized by a unique value of the critical current density, independent of the magnetic history of the sample. The results support a recent phenomenological model proposed by Ravikumar et al. [Phys. Rev. B 61 (2000) R6479] which postulates a specific recipe to incorporate the history dependence of the current density. Our data also shows the occurrence of a first order phase transition from an ordered vortex phase to a disordered phase across the PE. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(00)01772-X

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We succeeded in growing single crystals of TmAl3 with the AuCu3-type cubic structure, This compound is a reference for a heavy-fermion compound YbAl3. The single crystals were grown by the self-flux method. We observed de Haas-van Alphen oscillation. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)01133-1

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We have succeeded in observing the de Haas-van Alphen (dHvA) oscillations in the filled skutterudite PrFe4P12. The results predict a large difference in topology of the Fermi surface compared to the reference compound LaFe4P12. The cyclotron effective mass is found to be extraordinarily enhanced with the maximum value of 67m(0). (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00764-2

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Scanning tunneling microscopy and scanning tunneling spectroscopy measurements have been performed on a single crystal of CeRu(2) down to 2.2 K under a magnetic field up to 2.0 T. The sample surfaces for the measurements are prepared by cutting or cracking the single crystal at 4.2 K. The vortex lattice has been imaged by mapping the quasiparticle density of states at the Fermi energy on the surface. We have observed that the surface has been covered with microstructures a few nm in diameter. These microstructures are characteristic of the surface when the sample is cut or cracked at low temperature.

DOI： 10.1007/s003390100657

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We measured the transverse magnetoresistance and de Haas-van Alphen (dHvA) oscillation in the ferromagnetic compounds U3As4 and U3P4 The magnetoresistance in both compounds increases as a function of H-n (n similar or equal to 2) in a wide angular region, indicating that U3As4 and U3P4 are compensated metals. As for U3P4 the angular dependence of the magnetoresistance shows clearly dips for particular field directions. This implies the existence of a multiply-connected Fermi surface which favors open orbits along the [110] and [112] directions. We also detected several dHvA branches in U3As4 and U3P4 Most Of them are due to the closed Fermi surfaces, which are explained by recent results of fully relativistic spin-polarized LMTO band calculations. The cyclotron effective mass is large, ranging from 5 to 70 mo, and consistent with the electronic specific heat coefficient of 83 mJ/K-2.mol in U3As4 and 90 mJ/K-2.mol in U3P4.

DOI： 10.1143/JPSJ.70.558

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We observed the de Has-van Alphen oscillation in the heavy fermion compound CeIrIn5. The topology of the Fermi surface is found to be nearly cylindrical, reflecting the unique tetragonal structure. Observed branches are well explained bg the 4f-itinerant band model. The cyclotron masses of 20-30m(0) are one order larger than the corresponding band masses.

DOI： 10.1103/PhysRevB.63.060503

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We grew a high-quality single crystal of UC and carried out the de Haas-van Alphen (dHvA) experiments. The Fermi surfaces of a semimetal UC were confirmed to consist of three ellipsoidal hole-Fermi surfaces centered at the X points and six cushion-like electron-Fermi surfaces centered at the W points in the FCC Brillouin zone. These Fermi surface properties are clarified on the basis of the combined results of dHvA experiments and SRAPW-energy band calculations. The hole and electron Fermi surfaces mainly originate from the C-2p valence band and the U-5f conduction band, respectively. The cyclotron mass of the hole is light, being a rest mass of an electron m0, while the mass of the electron is heavy, being in the range from 4.0 to 15m0. The mass enhancement is large for the electron Fermi surface, originated from the U-5f character. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00621-1

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We measured de Haas-van Alphen oscillation in UPd2Al3 in order to reveal heavy electronic states at low temperatures down to 40 mK. For this purpose, we grew a high-quality single crystal using a purified uranium metal. All the branches reported in the previous work were observed in this study. In addition, we observed a new branch zeta with an extremely large cyclotron mass 65m(0). The dHvA frequency 9.96 x 10(7) Oe for branch zeta coincides with the band calculations based on the itinerant 5f electron picture. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)02566-1

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A self-consistent band calculation including an orbital polarization is performed for ferromagnetic UGa2 on the basis of an all-electron fully-relativistic spin-polarized LAPW (RSPLAPW) method with exchange-correlation potentials in a local density approximation (LDA). The obtained magnetic moment is composed of the spin of about -2.0 μB and the orbital moment of about 4.9 μB. Accordingly, it can be interpreted as if the configuration were a localized 5f2, though the f character contains about 2.5 as valence electrons. From the band structure, the Fermi surface is constructed in order to analyze frequencies observed by the de Haas-van Alphen (dHvA) effect.

DOI： 10.1016/S0921-4526(99)01217-X

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We have grown single crystals of UGa3, USb2 and UBi2 by the self-flux method and measured the de Haas-van Alphen (dHvA) oscillations. The detected Fermi surfaces were five closed ones in an antiferromagnetic compound UGa3. The cylindrical Fermi surfaces were observed for USb2 and UBi2, which manifests the two-dimensional character on the conduction electrons.

DOI： 10.1016/S0921-4526(99)00843-1

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An intermediate valence compound CeNi exhibits a phase transition under pressure, which is associated with the γ-α transition in Ce. To clarify a change of the electronic state under pressure, we measured the de Haas-van Alphen (dHvA) effect under pressure up to 6 kbar using a Cu-Be pressure cell. The dHvA branches are still observed after the phase transition. The topology of the Fermi surface is therefore unchanged. The cyclotron effective mass is, however, reduced from 11 to 3.2 m0 for branch ε and from 5.4 to 1.2 m0 for branch σ when the pressure is changed from 1 bar to 3.7 kbar.

DOI： 10.1016/S0921-4526(99)00844-3

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DOI： 10.1143/JPSJ.70.538

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We have investigated the superconducting gap of CeRu2 by point-contact spectroscopy and obtained its magnetic field dependences. Wt experiments were performed both for single iud polycrystals. We superconducting gap value is up to 30 % greater for the single crystal than in the polycrystalline CeRu2. We gap decreases almost linearly with the increasing field and vanishes at the characteristic field H-c* close to the irreversibility one. For the single crystalline sample there am some deviations from linear behaviour of the gap in the region of H-c*. Zero-bias maximum growth of differential resistance was often observed above H-c*.

DOI： 10.1142/9789812793676_0048

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Physical Society of Japan (JPS)  

We grew a high-quality single crystal of UC and carried out the de Haas-van Alphen(dHvA) experiments.The Fermi surfaces of a semimetal UC were confirmed to consist of three ellipsoidalhole-Fermi surfaces centered at the X points and six cushion-like electron-Fermisurfaces centered at the W points in the fcc Brillouin zone.These Fermi surface properties are based on the combined results of dHvA experimentsand SRAPW-energy band calculations.The hole and electron Fermi surfaces mainly originate from the C 2p valenceband and the U 5f conduction band, respectively.The cyclotron mass of the hole is light, being a rest mass of an electron m0,while the mass of the electron is heavy, being in the range from 4.0 to 15 m0.The mass enhancement is large for the electron Fermi surface, originated fromthe U 5f character.

DOI： 10.1143/JPSJ.68.3953

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The de Haas-van Alphen (dHvA) oscillation was observed clearly in both the normal and superconducting mixed states in NbSe2, CeRu2, URu2Si2, and UPd2Al3. The dHvA frequency, which is proportional to the extremal cross-sectional area of the Fermi surface, does not change in magnitude between the normal and mixed states. For the f-electron superconductors, the cyclotron effective mass is found to be reduced and the corresponding Dingle temperature or scattering rate of the conduction electron increases in the mixed state. An anisotropic energy gap with a line node for URu2Si2 and UPd2Al3 is discussed from the angular dependence of the dHvA amplitude in the mixed state. (C) 1999 American Institute of Physics.

DOI： 10.1063/1.593787

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We have succeeded in growing a high-quality single crystal of URu2Si2 with a residual resistivity ratio of 255 and performed magnetoresistance and de Haas–van Alphen (dHvA) experiments. The dHvA oscillations were observed clearly in both the normal and superconducting mixed states. From the magnetoresistance experiments, it is concluded that URu2Si2 is a compensated metal with equal carrier numbers of electrons and holes. In the dHvA experiments we observed three kinds of Fermi surfaces. We studied precisely the Fermi surface properties in both the normal and mixed states. The dHvA frequency does not change in magnitude between the normal and mixed states, while the cyclotron effective mass is reduced, and the corresponding Dingle temperature or scattering rate of the conduction electron increases in the mixed state. © 1999 Taylor and Francis Group, LLC.

DOI： 10.1080/13642819908214859

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We succeeded in growing high-quality single crystals of CeRu2 and URu2Si2 and observed the de Haas-van Alphen (dHvA) oscillations in both the normal and superconducting mixed states. The dHvA frequency does not change in magnitude between the normal and superconducting mixed states, while the cyclotron mass is reduced, and the corresponding Dingle temperature or the scattering rate of the conduction electron increases in the mixed state. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)01164-8

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Language：English   Publisher：Japanese Journal of Applied Physics  

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We observed the de Haas-van Alphen (dHvA) oscillation of UB2 with a hexagonal structure. All of the detected dHvA branches, which are about seven in number, are detected in the limited angle regions. The cyclotron masses are moderately heavy, ranging from 1.2 to 7.7 m0. These features of the Fermi surface are well explained by the 5f-itinerant band theory. © 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)01085-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

We have grown high-quality single crystals of tetragonal USb2 using a flux method. We have detected five branches in de Haas-van Alphen (dHvA) experiments. Frequencies of all dHvA branches follow the 1/ cos θ-dependence, revealing the presence of cylindrical Fermi surfaces, where θ is a tilt angle from [001] to [100]. The cyclotron masses are in the range from 1.84 to 8.33 m0. The two-dimensional Fermi surfaces are due to the conduction electrons in the U-plane, including the itinerant 5f-electrons.

DOI： 10.1143/JPSJ.68.2182

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We have measured the electrical resistivity, thermoelectric power, magnetic susceptibility, magnetoresistance and specific heat of a Pauli paramagnetic compound UB2. The magnetoresistance shows an extremely large H2-dependence for any field directions, indicating a compensated metal without an open orbit. This result is consistent with the results of the dHvA experiment and 5f-itinerant band calculation.

DOI： 10.1143/JPSJ.68.972

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We have observed the de Haas-van Alphen (dHvA) oscillations in SmPb3, GdPb3, EuPb3 and YbPb3. Detected dHvA branches are discussed on the basis of the result of the FLAPW band calculation. © 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)00938-7

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The high-resolution photoemission spectroscopy study of single crystalline CeNiSn indicates a finite density of states at EF, implying a semi-metallic ground state. This finding is supported by the lineshape analysis using the DOS models. The Ce 4f spectrum exhibits three peak structures, in which the peak near-EF is found to reflect a substantially large Ce 4f-Sn sp hybridization. © 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)00821-7

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A huge peak of irreversible magnetization in CeRu2 single crystal, together with the equilibrium magnetization, was investigated by means of a static magnetization measurement using a Faraday force magnetometer. The residual resistance ratio of the used crystal exceeds 250, indicating that it is a clean superconductor. Contrary to the previous reports, there is no pinning-free region in the magnetization curves below the upper critical field Hc2. The detailed minor-hysteresis-loop measurement has revealed that the peak structure in the increasing-field magnetization curve around the onset field of the peak strongly depends on previous field-history, resulting in an apparent asymmetry of the peak structure. No trace of paramagnetic suppression of superconductivity in the vortex-penetrated state is observed from the superconducting equilibrium magnetization curves. The peak position, although highly anisotropic. can be interrelated to the peak strength, regardless of the applied field direction. It is likely that the irreversibility peak is due to a synchronization pinning of the defective flux line lattice, rather than due to a first-order transition from the mixed state to the Fulde-Ferrell-Larkin-Ovchinnikov state.

DOI： 10.1143/JPSJ.68.224

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CeRu2 and 2H-NbSe2 display remarkable similarities in their magnetic response, reflecting the manner in which the weakly pinned flux link lattice (FLL) loses spatial order in the peak-effect (PE) regime. We present evidence for discontinuous changes in the screening response near the onset of the PE in these systems, and demonstrate history-dependent effects. We attribute these features to a disorder-induced fracturing and entanglement of the FLL, as an alternative to the appearance of a spatially modulated ground state for CeRu2. [S0163-1829(98)05725-7].

DOI： 10.1103/PhysRevB.58.995

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A study of path dependent effects in single crystals of CeRu2 and 2H-NbSe2 shows that critical current density J(c) of the vortex state depends on its thermomagnetic history over a very large part of (H,T) parameter space. The path dependence in J(c) is absent above the peak position (i.e., H>H-p) of the peak effect region, which we believe identifies the complete loss of order in the vortex structure. The highly disordered field cooled (FC) state can be healed into a relatively ordered vortex lattice by subjecting it to a large enough change in de field (few tens of Oe) or by shaking the field cooled state with sufficient ac field (few Oe).

DOI： 10.1103/PhysRevB.57.R11069

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We have succeeded in growing high-quality single crystals of CeRu2 and have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in both its normal and its superconducting mixed states. From the result of the magnetoresistance, we conclude that CeRu2 is a compensated metal. The measured dHvA frequencies are well explained by the results of band-structure calculations. The dHvA frequency does not change in magnitude between the normal and superconducting mixed states, while the cyclotron mass is reduced, and the corresponding Dingle temperature increases in the mixed state. The mass and the Dingle temperature strongly depend on the magnetic field in the mixed state.

DOI： 10.1080/13642819808206399

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The quantum oscillation of symmetrized elastic moduli of CeRu2 has been measured by an ultrasonic technique not only in the normal conducting state but also in the superconducting mixed state which includes the field region where a peak effect appears in the magnetization curve. The angular dependence of the oscillation frequencies for various branches in the normal state is identical to that previously obtained from a magnetic dHvA experiment by Hedo et al. The angular dependence of the quantum-oscillation amplitude is discussed in terms of the electron-phonon coupling. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00339-9

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Vortex phase diagram and peak effect have been investigated by the magnetization measurements for various CeRu2 samples with different quality. The peak effect survives even in the extremely qualified samples and in the magnetic field H∥〈1 1 1〉. Field dependence of the anomalous magnetization reveals that the strong-pinning region terminates at H* = 24 kOe and T* = 4.0 K, independent of the quality of sample. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00396-X

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We have determined the Fermi surface properties of PrPb3 by a de Haas-van Alphen experiment. The cyclotron effective mass is extremely temperature dependent and highly anisotropic even for almost spherical Fermi surfaces, which is due to the antiferroquadrupolar ordering. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00931-1

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A study of path dependent effects in single crystals of (Formula presented) and (Formula presented) shows that critical current density (Formula presented) of the vortex state depends on its thermomagnetic history over a very large part of (Formula presented) parameter space. The path dependence in (Formula presented) is absent above the peak position (i.e., (Formula presented) of the peak effect region, which we believe identifies the complete loss of order in the vortex structure. The highly disordered field cooled (FC) state can be healed into a relatively ordered vortex lattice by subjecting it to a large enough change in dc field (few tens of Oe) or by shaking the field cooled state with sufficient ac field (few Oe). © 1998 The American Physical Society.

DOI： 10.1103/PhysRevB.57.R11069

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We have succeeded in growing high-quality single crystals of CeRu2 and have observed dHvA oscillations both in the normal and superconducting vortex (mixed) states. The detected dHvA frequencies have been well explained by the result of band-structure calculations. The dHvA frequency does not change in magnitude between the normal and superconducting states, while the cyclotron mass is reduced and the Dingle temperature is enhanced in the vortex state. The mass and the Dingle temperature depend on the magnetic field in the vortex state. © 1998 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(97)00917-7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

We have measured the specific heat and the magnetization in the superconducting mixed state of CeRu2 at low temperatures and in high magnetic fields. We have clarified a rich variety of superconducting properties such as the temperature dependence of the electronic specific heat and Maki parameters κ1, κ2 and κ3. From these experimental results, CeRu2 is concluded to be of the BCS-type in superconductivity. Nevertheless, interesting is the magnetic field dependence of the electronic specific heat at 0.5 K, indicating a √H like behavior in low fields and a H-linear dependence in high fields up to the upper critical field of 50 kOe. This characteristic specific heat is discussed on the basis of a microscopic theory by Brandt et al.

DOI： 10.1143/JPSJ.67.272

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We grew a single crystal of UB2 with the hexagonal structure and observed the de Haas-van Alphen (dHvA) oscillation. All of the dHvA branches, which are about seven in number, are detected in the limited angle regions. They are well explained by the 5f-itinerant relativistic band theory with an exchange and correlation potential in a local density approximation. Namely, UB2 is a compensated metal with an equal number of electron and hole. The Fermi surface consists of two closed but corrugated Fermi surfaces. The cyclotron masses are moderately heavy, ranging from 1.2 to 7.7m0.

DOI： 10.1143/JPSJ.67.3171

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We present data of the elastic properties of the Laves phase compound CeRu2 in the normal and superconducting state obtained from ultrasound measurements. In the temperature range between the superconducting transition temperature of 6.1 K and 300 K we used a deformation potential coupling approach to describe the temperature dependence of the elastic constants. The elastic anomalies in the superconducting state are characterised with the model of thermally assisted flux flow (TAFF). This enables us to construct a detailed superconducting B-T phase diagram including the vortex dynamics and interpret the peak effect region. Especially the ultrasonic measurements exhibit clearly the connectin between the normal state and the superconducting properties. They slow that structural fluctuations have strong effects on the superconductivity and on the vortex dynamics.

DOI： 10.1007/BF02397466

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Detailed magnetisation measurements are presented for a cubic Laves phase superconducting single crystal CeRu2. These measurements have been performed in the peak effect regime using Quantum Design SQUID Magnetic Property Measurement System (MPMS). To understand the influence of magnetic field inhomogeneity of this set up, on the measured magnetisation, all the data is recorded for different scan lengths. We clearly demonstrate that some of the anomalous magnetisation results reported in literature are artefacts of field inhomogeneity. We also present a model based on Critical State Model to simulate the effect of field inhomogeneity on the measured magnetisation.

DOI： 10.1016/S0921-4534(97)00039-7

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We have measured the magnetoresistance at high fields up to 15 T and at low temperatures down to 0.4 K for CeNiSn with the orthorhombic structure. The longitudinal magnetoresistance (J parallel to H) is small in magnitude for the magnetic field H parallel to b- and c-axis. On the other hand, the positive magnetoresistance is found to become dominant with the decrease of temperature for H parallel to b- and c-axis in the transverse configuration (J perpendicular to H). For H parallel to a, the magnetoresistance is negative for any current direction. These experimental results have been discussed on the basis of the cyclotron motion of the compensated carriers with closed Fermi surfaces and the reduction of the anisotropic hybridization gap.

DOI： 10.1016/S0921-4526(96)00804-6

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Language：English   Publisher：PHYSICAL SOC JAPAN  

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) oscillation of URu2Si2. From the results of the magnetoresistance measurement, URu2Si2 is concluded to be a compensated metal with closed Fermi surfaces. The dHvA branch, which corresponds to a nearly spherical Fermi surface, has been detected in both the normal and superconducting mixed states. The Dingle temperature or the electron scattering rate is found to be strongly enhanced and the cyclotron effective mass to be correspondingly reduced in the mixed state. © 1997, THE PHYSICAL SOCIETY OF JAPAN. All rights reserved.

DOI： 10.1143/JPSJ.66.945

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We have succeeded in growing high-quality single crystals of CeRu2 and have observed dHvA oscillations both in the normal and superconducting mixed states. The detected dHvA frequencies, i.e. extremal cross-sectional areas of Fermi surfaces have been well explained by band structure calculations. The dHvA frequency between the normal and superconducting states does not change in magnitude, while the Dingle temperature increases in the mixed state. The cyclotron mass is found to become a little smaller in the mixed state than in the normal state.

DOI： 10.1016/S0921-4526(97)00105-1

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We have determined the lower and upper critical fields, Hc1 and Hc2 by measuring the DC magnetization, the AC susceptibility and the resistivity in fields for a superconductor U6Fe. The coherence length and the penetration depth are estimated as 50 and 2060 Å, respectively.

DOI： 10.1016/S0921-4526(96)00732-6

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Elastic moduli of high-quality single-crystalline CeRu2 have been measured between 2 and 300 K by an ultrasonic technique. Both shear moduli of (C11 - C12)/2 and C44 show a giant softening without structural transition. In contrast to the shear moduli, the bulk modulus CB indicates a normal temperature dependence without the anomalous softening. These results reveal that there exists a remarkable structural fluctuation corresponding to shearing strain in the normal state of CeRu2. The analysis taking account of the deformation potential coupling between the strain and an electronic energy band demonstrates that degenerate and peaked density of states is responsible for the softening.

DOI： 10.1016/S0921-4526(96)00582-0

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We have succeeded in growing a high-quality single crystal of CeRu2 and dHvA oscillations have been clearly observed both in the normal and mixed states. The dHvA amplitude of a small dHvA frequency is reduced a little in the mixed state compared to that in the normal state, while that of a large dHvA frequency is reduced strongly. The cyclotron mass is found to become a little smaller in the mixed state than that in the normal state, although the cross-sectional area of the Fermi surface is unchanged from the normal state.

DOI： 10.1016/S0921-4526(96)00730-2

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Superconducting property of single crystalline UPd2Al3 has been studied by static magnetization, AC susceptibility and flux flow resistivity measurements. A pronounced peak structure is observed just below the superconducting upper critical field HC2. The peak consists of two structures at low temperatures, becomes one above 0.6 K and continues up to a low field of 0.1 T. These results are compared to those based on the FFLO model.

DOI： 10.1016/S0921-4526(96)00720-X

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We have measured the electrical resistivity, Hall effect and transverse even voltage in the flux-flow state of CeRu2, CeCo2 and Yb3Rh4Sn13. In all the transport properties, we found a clear anomaly related with the peak effect, which was argued in relation to the inhomogeneous superconducting phase proposed by Fulde-Ferrell and Larkin-Ovchinnikov. The pinning force and the transverse even voltage depend largely on sample quality. A deviation from the ordinary BCS prediction, suggesting an anisotropy in the superconducting gap, has been found in the specific heat of CeCo2.

DOI： 10.1016/S0921-4526(96)00734-X

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New magnetisation results on a clean crystal of cubic CeRu2 reveal that the magnetisation hysteresis anomaly below Hc2(T) involves two distinct steps.

DOI： 10.1016/S0921-4534(97)01112-X

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Language：English   Publisher：The Physical Society of Japan (JPS)  

Single crystals of superconducting U6Fe were grown by both thezone-melting method and the Czochralski pulling method.The upper critical field Hc2 was determined from the electrical resistivityin applied magnetic fields, and Hc2 is found to be anisotropic;13.1 T for the field along the [001] directionand 10.4 T for [110]. Anisotropy of Hc2 is well explained by the effective mass model.

DOI： 10.1143/JPSJ.65.1034

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We report experimental results of electrical resistivity, de Haas-van Alphen effect, specific heat and thermal expansion of UPd2Al3. The nominal composition is denoted by the formula of UPd2+xAl3+y. Samples with the composition of UPd2Al3.03 and UPd2.02Al3.03 reveal de Haas-van Alphen oscillations of the magnetic susceptibility. An anomaly is observed in the superconducting phase in the temperature dependence of the specific heat and thermal expansion of UPd2Al3.03. The relation between the sample quality and the appearance of the anomaly is discussed.

DOI： 10.1109/20.312209

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DOI： 10.11316/jpsgaiyo.72.2.0_2895

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DOI： 10.20653/pesj.64.2_127

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DOI： 10.11316/jpsgaiyo.67.2.3.0_523_4

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We report B-11 and Pt-195 NMR measurements in noncentrosymmetric superconductor Li2Pt3B. We find that the spin susceptibility measured by the Knight shift remains unchanged across the superconducting transition temperature T-c. With decreasing temperature (T) below T-c, the spin-lattice relaxation rate 1/T-1 decreases with no coherence peak and is in proportion to T-3. These results indicate that the Cooper pair is in the spin-triplet state and that there exist line nodes in the superconducting gap function. They are in sharp contrast to those in the isostructural Li2Pd3B which is a spin-singlet, s-wave superconductor, and are ascribed to the enhanced spin-orbit coupling due to the lack of spatial inversion symmetry. Our finding points to a new paradigm where exotic superconductivity arises in the absence of electron-electron correlations.

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Language：Japanese   Publisher：物性研究刊行会  

この論文は国立情報学研究所の電子図書館事業により電子化されました。

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