研究者詳細 - 鄭　国慶

論文 - 鄭　国慶

分割表示 265 件中 181 - 200 件目／全件表示 >>

Delocalized Quasiparticles in the Vortex State of an Overdoped High- [Formula presented] Superconductor Probed by [Formula presented] NMR 査読

G. q. Zheng, H. Ozaki, Y. Kitaoka, P. Kuhns, A. P. Reyes, W. G. Moulton

Physical Review Letters 88 ( 7 ) 4 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report the spin Knight shift ([Formula presented]) and the nuclear spin-lattice relaxation rate ([Formula presented]) in the vortex state as a function of magnetic field ([Formula presented]) up to 28 T in the high- [Formula presented] superconductor [Formula presented] ([Formula presented]). At low temperatures well below [Formula presented], both [Formula presented] and [Formula presented] measured around the middle point between the two nearest vortices (saddle point) increase substantially with increasing field, which indicate that the quasiparticle states with an ungapped spectrum are extended outside the vortex cores in a [Formula presented]-wave superconductor. The density of states (DOS) around the saddle point is found to be [Formula presented], with [Formula presented] and [Formula presented] being the normal-state DOS. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevLett.88.077003

(formula presented)-NQR evidence for unconventional superconductivity in (formula presented) under pressure 査読

S. Kawasaki, T. Mito, Y. Kawasaki, G. Zheng, Y. Kitaoka, H. Shishido, S. Araki, R. Settai, Y. Ōnuki

Physical Review B - Condensed Matter and Materials Physics 66 ( 5 ) 1 - 4 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report evidence for unconventional superconductivity in (formula presented) at a pressure (formula presented) above the critical pressure (formula presented) revealed by measurements of the nuclear-spin-lattice-relaxation time (formula presented) and ac susceptibility (ac- (formula presented) Both measurements of (formula presented) and ac- (formula presented) have pointed to a superconducting transition at (formula presented) which is much lower than the onset temperature (formula presented) at zero resistance. The temperature dependence of (formula presented) shows no coherence peak just below (formula presented) indicative of an unconventional nature for the superconductivity induced in (formula presented). © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.054521

Pressure-temperature phase diagram of antiferromagnetism and superconductivity in (formula presented) and (formula presented) (formula presented) study under pressure 査読

S. Kawasaki, T. Mito, G. Zheng, C. Thessieu, Y. Kawasaki, K. Ishida, Y. Kitaoka, T. Muramatsu, T. C. Kobayashi, D. Aoki, S. Araki, Y. Haga, R. Settai, Y. Onuki

Physical Review B - Condensed Matter and Materials Physics 65 ( 2 ) 1 - 4 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report the pressure (formula presented)-temperature (formula presented) phase diagram of antiferromagnetism and superconductivity in (formula presented) and (formula presented) revealed by the (formula presented) nuclear-spin-lattice-relaxation (formula presented) measurement. In the itinerant magnet (formula presented) we found that the Néel temperature (formula presented) is reduced at (formula presented) with an emergent pseudogap behavior. In (formula presented) the localized magnetic character is robust against the application of pressure up to (formula presented) beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations. © 2001 The American Physical Society.

DOI： 10.1103/PhysRevB.65.020504

Superconducting and magnetic characteristics in the multilayered high-(formula presented) cuprates (formula presented) with (formula presented) probed by Cu and Tl NMR: High value for (formula presented) 査読

H. Kotegawa, Y. Tokunaga, K. Ishida, G. Q. Zheng, Y. Kitaoka, A. Iyo, Y. Tanaka, H. Ihara

Physical Review B - Condensed Matter and Materials Physics 65 ( 18 ) 1 - 4 2002年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report (formula presented) and (formula presented) nuclear magnetic resonance (NMR) measurements on trilayered high-(formula presented) compounds (formula presented) (Tl-1223) that were synthesized at a high pressure and exhibits a high value of superconducting (SC) transition temperature (formula presented) In the SC state, the nuclear spin-lattice relaxation rate (formula presented) reveals a (formula presented) behavior below (formula presented) followed by a (formula presented) behavior at very low temperatures. The results are accounted for by the d-wave pairing model where the presence of the residual density of the states (formula presented) is incorporated at the Fermi level to be consistent with the experiments. The important finding is that the size [in (formula presented) is much smaller for the present compounds of Tl-1223 with (formula presented) than for the previous Tl-2223. Correspondingly, it is shown that an NMR intensity at a satellite peak in the Tl-NMR spectrum, which originates from a possible substitution of Tl for Ca, is much smaller for the former than for the latter. The synthesis technique at a high pressure is found to be a good way to remove such a crystal imperfection due to Tl/Ca intersubstitution. We have demonstrated from a microscopic point of view that as a result of decreasing the degree of disorder effect, the (formula presented) in Tl-1223 has revealed a value higher than 130 K. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.65.184504

Characterizing the pseudogap in the high-Tc superconductors using very high magnetic fields: Implications on the phase diagram

Guo-Qing Zheng, H. Ozaki, Y. Kitaoka, W. G. Clark, Y. Kodama, T. Kondo, Y. Shimakawa, Y. Kubo, P. Kuhns, A. P. Reyes, W. G. Moulton

Physica C: Superconductivity and its Applications 364-365 458 - 461 2001年11月

記述言語：英語掲載種別：研究論文（学術雑誌）

We find contrastive response of the pseudogap (PG) to high magnetic fields up to 28.5 T based on 63Cu NMR measurements. In the slightly overdoped TlSr2CaCu2O6.8, the PG is strongly field dependent and shown to be due to the superconducting fluctuations. By contrast, the PG in the underdoped YBa2Cu4O8 does not depend on magnetic fields up to 28.5 T. These results imply that there exists a field-insensitive PG up to a certain doping level beyond which it is taken over by the superconducting fluctuations-induced one. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(01)00820-6

Comment on "Magnetic-field-induced low-energy spin excitations in YBa2Cu4O8 as measured by high field Gd3+ electron spin resonance”

G.-q. Zheng, Y. Kitaoka, W. G. Clark

Phys. Rev. Lett. 87 ( 20 ) 2001年11月

Characterizing the pseudogap in the high-T-c superconductors using very high magnetic fields: implications on the phase diagram 査読

GQ Zheng, H Ozaki, Y Kitaoka, WG Clark, Y Kodama, T Kondo, Y Shimakawa, Y Kubo, P Kuhns, AP Reyes, WG Moulton

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 364 458 - 461 2001年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We find contrastive response of the pseudogap (PG) to high magnetic fields up to 28.5 T based on Cu-63 NMR measurements. In the slightly overdoped TlSr2CaCu2O6.8, the PG is strongly field dependent and shown to be due to the superconducting fluctuations. By contrast, the PG in the underdoped YBa2CU4O8 does not depend on magnetic fields up to 28.5 T. These results imply that there exists a field-insensitive PG up to a certain doping level beyond which it is taken over by the superconducting fluctuations-induced one. (C) 2001 Elsevier Science B.V. All rights reserved.

Unusual magnetic and superconducting characteristics in multilayered high-Tc cuprates: 63Cu NMR study

H. Kotegawa, Y. Tokunaga, K. Ishida, G. Q. Zheng, Y. Kitaoka, H. Kito, A. Iyo, K. Tokiwa, T. Watanabe, H. Ihara

Physical Review B - Condensed Matter and Materials Physics 64 ( 6 ) 645151 - 645155 2001年8月

記述言語：英語掲載種別：研究論文（学術雑誌）

We report unusual magnetic and superconducting (SC) characteristics in multilayered CuO2 planes in Hg- and Cu-based high-Tc cuprates through the 63Cu-NMR measurements. These compounds, in which the number of CuO2 planes (n) ranges from 3 to 5 in a unit cell, include crystallographically inequivalent outer (OP) and inner (IP) CuO2 plane that are surrounded by pyramidal and square oxygen, respectively. The Knight shift (63K) at the OP and IP exhibits respective characteristic temperature dependence, consistent with its own doping level. Using an experimental relation between the spin part in 63K at room temperature and the doping level in a CuO2 layer Nh, we show that Nh(OP) at the OP is larger than Nh(IP) at the IP for all the systems and its difference ΔNh=Nh(OP)-Nh(IP) increases as either a total carrier content σ or n increases. At ΔNh's exceeding a critical value, the pseudogap behavior in the normal state is seen alone at the IP, and a bulk SC transition does not set in simultaneously at the IP and OP. A SC nature at the OP becomes consistent with a mean-field behavior only below Tc2 that is significantly lower than Tc. Reduction in Tc with increasing n is associated with an increase in ΔNh. It is a rather remarkable aspect that a Tc is not always reduced even though these multilayered high-Tc compounds are heavily overdoped. This arises, we show, because the IP remains underdoped and keeps a high value of Tc, while the OP is predominantly overdoped. This may be a microscopic origin for the lowest anisotropic SC characteristics reported to date in Cu-based multilayered high-Tc compounds.

DOI： 10.1103/PhysRevB.64.064515

Unusual magnetic and superconducting characteristics in multilayered high-T-c cuprates: Cu-63 NMR study 査読

H Kotegawa, Y Tokunaga, K Ishida, GQ Zheng, Y Kitaoka, H Kito, A Iyo, K Tokiwa, T Watanabe, H Ihara

PHYSICAL REVIEW B 64 ( 6 ) 1 - 5 2001年8月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report unusual magnetic and superconducting (SC) characteristics in multilayered CuO2 planes in Hg- and Cu-based high-T-c cuprates through the Cu-63-NMR measurements. These compounds, in which the number of CuO2 planes (n) ranges from 3 to 5 in a unit cell, include crystallographically inequivalent outer (OP) and inner (IP) CuO2 plane that are surrounded by pyramidal and square oxygen, respectively. The Knight shift (K-63) at the OP and IP exhibits respective characteristic temperature dependence, consistent with its own doping level. Using an experimental relation between the spin part in K-63 at room temperature, and the doping level in a CuO2 layer N-h, we show that N-h,(OP) at the OP is larger than Nh(IP) at the IP for all the systems and its difference DeltaN(h)=N-h(OP) -N-h(IP) increases as either a total carrier content delta or n increases. At DeltaN(h)'s exceeding a critical value, the pseudogap behavior in the normal state is seen alone at the IP. and a bulk SC transition does not set in simultaneously at the IP and OP. A SC nature at the OP becomes consistent with a mean-field behavior only below T-c2 that is significantly lower than T-c. Reduction in T-c with increasing n is associated with an increase in DeltaN(h). It is a rather remarkable aspect that a T-c is not always reduced even though these multilayered high-T-c compounds are heavily overdoped. This arises, we show, because the IP remains underdoped and keeps a high value of T-c, while the OP is predominantly overdoped. This may be a microscopic origin for the lowest anisotropic SC characteristics reported to date in Cu-based multilayered high-T-c compounds.

Pressure-induced anomalous magnetism and unconventional superconductivity in CeRhIn5: In-115-NQR study under pressure

T Mito, S Kawasaki, GQ Zheng, Y Kawasaki, K Ishida, Y Kitaoka, D Aoki, Y Haga, Y Onuki

PHYSICAL REVIEW B 63 ( 22 ) 2001年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report In-115 nuclear-quadrupole-resonance (NQR) measurements of the pressure(P)-induced superconductor CeRhIn5 in the antiferromagnetic (AF) and superconducting (SC) states. In the AF region, the internal field H-int at the In site is substantially reduced from H-int= 1.75 kOe at P=0 to 0.39 kOe at P=1.23 GPa, while the Neel temperature slightly changes with increasing P. This suggests that either the size in the ordered moment M-Q(P) or the angle theta(P) between the direction of M-Q(P) and the tetragonal c axis is extrapolated to zero at P*=1.6+/-0.1 GPa at which a bulk SC transition is no longer emergent. In the SC state at P=2.1 GPa, the nuclear spin-lattice relaxation rate (115)(1/T-1) has revealed a T-3 dependence without the coherence peak just below T-c, giving evidence for the unconventional superconductivity. The dimensionality of the magnetic fluctuations in the normal state is also discussed.

Electrical transport and low-field magnetoresistance in the series of mixed polycrystals (1-m)La2/3Ca1/3MnO3+mLa(2/3)Sr(1/3)MnO(3) 査読

SL Yuan, GQ Zhang, G Peng, F Tu, XY Zeng, J Liu, YP Yang, Y Jiang, CQ Tang

JOURNAL OF PHYSICS-CONDENSED MATTER 13 ( 24 ) 5691 - 5697 2001年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：IOP PUBLISHING LTD

The perovskites of La2/3Ca1/3MnO3 (LCMO) and La2/3Sr1/3MnO3 (LSMO) were synthesized by the sol-gel method. The two perovskites were mixed into polycrystalline materials, (1 - m)LCMO + mLSMO, where m is the relative weight ratio of LSMO. The compound with m similar to 0.3-0.5 has the lowest semiconductor-metal transition temperature T-p and the largest low-T resistivity. Moving away from this ratio, T-p increases while the low-T resistivity decreases with increasing or decreasing m. Measurements of the magnetoresistance (MR) show that the mixed polycrystals exhibit a sizable MR effect in low magnetic fields which increases upon cooling and reaches its largest value for T --> 0 K. It is also interesting to observe the almost T-independent MR effect over a wide temperature window below 300 K for the mixed materials with smaller m.

Exotic magnetic and superconducting phases in CeCU2Si2 close to magnetically ordered state: Cu-NQR study

Y Kawasaki, K Obinata, K Ishida, T Mito, GQ Zheng, Y Kitaoka, C Geibel, F Steglich

JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS 226 374 - 375 2001年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：ELSEVIER SCIENCE BV

We report Cu-NQR results under pressure on heavy-fermion (HF) superconductor CeCu2Si2 close to a magnetic phase, Ce0.99Cu2.02Si2 and CeCu2(Si0.98Ge0.02)(2). It is found that an application of a minute pressure exceeding 0.3 GPa markedly suppresses low-energy magnetic fluctuations observed at ambient pressure (P = 0) in Ce0.99CU2.02Si2, Correspondingly, anomalous superconducting (SC) characteristics evolve into conventional HF-SC ones with increasing pressure. In the latter. the Ge substitution works as a negative chemical pressure. CeCu2(Si0.98Ge0.02)(2) reveals a magnetic phase transition at T-N = 0.75 K followed by the SC phase transition at T-c similar to 0.4 K at P = 0. It is suggested experimentally that the magnetic fluctuations seen in Ce0.99Cu2.02Si2 at P = 0 possesses a quantum critical character of both SC and magnetically ordered states. (C) 2001 Elsevier Science B.V. All rights reserved.

Unique spin dynamics and unconventional superconductivity in the layered heavy fermion compound CeIrIn5: NQR evidence

GQ Zheng, K Tanabe, T Mito, S Kawasaki, Y Kitaoka, D Aoki, Y Haga, Y Onuki

PHYSICAL REVIEW LETTERS 86 ( 20 ) 4664 - 4667 2001年5月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report measurements of the In-115 nuclear spin-lattice relaxation rate (1/T-1) between T = 0.09 and 100 K in the new heavy fermion (HF) compound CeIrIn5. Ar 0.4 less than or equal to T less than or equal to 100 K, 1/T-1 is strongly T-dependent, which indicates that CeIrIn5 is much more itinerant than known Ce-based HFs. We find that I/T1T, subtracting that for LaIrIn5, follows a (1 / tau + theta)(3/4) variation with theta = 8 K. We argue that this novel feature points to anisotropic, due to a layered crystal structure, spin fluctuations near a magnetic ordering. The hulk superconductivity sets in at 0.40 K below which the coherence peak is absent and 1/T-1 follows a T-3 variation, which suggests unconventional superconductivity with Line-node gap.

DOI： 10.1103/PhysRevLett.86.4664

Exotic superconducting phase in CeCu2Si2 close to antiferromagnetism: A Cu-NQR study under hydrostatic pressure

Y Kawasaki, K Ishida, T Mito, C Thessieu, GQ Zheng, Y Kitaoka, C Geibel, F Steglich

PHYSICAL REVIEW B 63 ( 14 ) 2001年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：AMER PHYSICAL SOC

We report Cu nuclear-quadrupole-resonance results under pressure (P) on a homogeneous CeCu2Si2 (T-c = 0.65 K) that revealed critical magnetic fluctuations at the border to an antiferromagnetic (AF) phase. This exotic superconducting (SC) phase evolves into the typical heavy-fermion SC phase at minute pressures exceeding P(c)similar to0.2 GPa. The nuclear spin-lattice relaxation data in a P range 0.85 - 2.58 GPa are shown to be accountable by the spin-fluctuation theory based on the nearly AF Ferni-liquid model. In 0 less than or equal toP<P-c<similar to>0.2 GPa, by contrast, we conclude that the exotic SC phase manifests itself under the unconventional normal state where AF waves propagate over a long range without any trace of AF order and thereby the heavy-fermion state breaks up.

Spin-gap and the superconducting fluctuations in high-T-c cuprates probed by Cu-63 NMR

GQ Zheng, H Ozaki, Y Kitaoka, WG Clark, Y Kodama, T Kondo, Y Shimakawa, Y Kubo, P Kuhns, AP Reyes, WG Moulton

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 62 ( 1-2 ) 25 - 27 2001年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

From the Cu-63 Knight shift and the nuclear spin-lattice relaxation rate under magnetic fields from zero up to 28 T in the underdoped (U) YBa2Cu4O8 and the slightly overdoped (O) TlSr2CaCu2O6.8 We find that the spin-gap (pseudogap) behaviors show contrasting response to magnetic fields in the U and O compounds. In the O compound. the spin-gap is strongly field dependent and can be accounted for by the superconducting fluctuation effects, but that in the U compound shows no field dependence. The implication is discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(00)00095-0

NMR study of carrier distribution and superconductivity in multilayered high-T-c cuprates

H Kotegawa, Y Tokunaga, K Ishida, GQ Zheng, Y Kitaoka, K Asayama, H Kito, A Iyo, H Ihara, K Tanaka, K Tokiwa, T Watanabe

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 62 ( 1-2 ) 171 - 175 2001年1月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：PERGAMON-ELSEVIER SCIENCE LTD

We report Cu-63-Knight shift measurement on multilayered high-T-c cuprate oxides that include inequivalent outer (OP) and inner (IP) CuO2 planes in a unit cell with number of planes n = 3-5. Using an experimental relation between the spin part of Knight shift (K-s) and the carrier concentration (N-h) reported in n = 1 and 2 cuprates, the local carrier concentrations Nh(OP) in the OP and Nh(IP) in the IP have been deduced. We have found that Nh(OP) is larger than Nh(IP) in all the systems. The difference in the doping level increases as total-carrier content delta and n increase. Imbalance between Nh(OP) and Nh(IP) is suggested to be caused by a mechanism that the electrostatic potential associated with the apical oxygen has more attraction for holes in the OP than in the IP. It is also suggested that T-c of Hg 1223 (n = 3) is the highest (T-c = 133 K) to date, due to N-h(IP) optimized to N-h.optimum similar to 0.2 From the fact that N-h(OP)> N-h.optimum, we propose that if Nh(OP) could also be optimized in addition to optimized N-h(IP). T-c might be raised higher than 133 K. (C) 2000 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(00)00122-0

NMR studies of strongly correlated superconductors

K. Asayama, Y. Kitaoka, G.-q. Zheng, K. Ishida, Y. Tokunaga

Annual Reports on NMR Spectroscopy 44, 75-142 ( 2001年

Pressure-induced anomalous magnetism and unconventional superconductivity in CeRhIn<inf>5</inf>: ¹¹⁵In-NQR study under pressure

T. Mito, S. Kawasaki, G. Q. Zheng, Y. Kawasaki, K. Ishida, Y. Kitaoka, D. Aoki, Y. Haga, Y. Onuki

Physical Review B - Condensed Matter and Materials Physics 63 ( 22 ) 2205071 - 2205074 2001年

掲載種別：研究論文（学術雑誌）

We report 115In nuclear-quadrupole-resonance (NQR) measurements of the pressure(P)-induced superconductor CeRhIn5 in the antiferromagnetic (AF) and superconducting (SC) states. In the AF region, the internal field Hint at the In site is substantially reduced from Hint = 1.75 kOe at P = 0 to 0.39 kOe at P = 1.23 GPa, while the Néel temperature slightly changes with increasing P. This suggests that either the size in the ordered moment MQ(P) or the angle θ(P) between the direction of MQ(P) and the tetragonal c axis is extrapolated to zero at P* = 1.6±0.1 GPa at which a bulk SC transition is no longer- emergent. In the SC state at P =2.1 GPa, the nuclear spin-lattice relaxation rate 115(1/T1) has revealed a T3 dependence without the coherence peak just below Tc, giving evidence for the unconventional superconductivity. The dimensionality of the magnetic fluctuations in the normal state is also discussed.

Pressure-induced anomalous magnetism and unconventional superconductivity in (formula presented) (formula presented)-NQR study under pressure 査読

Y. Kawasaki, Y. Onuki, G. q. Zheng, K. Ishida, Y. Kitaoka, S. Kawasaki, T. Mito, D. Aoki, Y. Haga

Physical Review B - Condensed Matter and Materials Physics 63 ( 22 ) 2001年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report (formula presented) nuclear-quadrupole-resonance (NQR) measurements of the pressure (formula presented)-induced superconductor (formula presented) in the antiferromagnetic (AF) and superconducting (SC) states. In the AF region, the internal field (formula presented) at the In site is substantially reduced from (formula presented) at (formula presented) to 0.39 kOe at (formula presented) while the Néel temperature slightly changes with increasing P. This suggests that either the size in the ordered moment (formula presented) or the angle (formula presented) between the direction of (formula presented) and the tetragonal c axis is extrapolated to zero at (formula presented) at which a bulk SC transition is no longer emergent. In the SC state at (formula presented) the nuclear spin-lattice relaxation rate (formula presented) has revealed a (formula presented) dependence without the coherence peak just below (formula presented) giving evidence for the unconventional superconductivity. The dimensionality of the magnetic fluctuations in the normal state is also discussed. © 2001 The American Physical Society.

DOI： 10.1103/PhysRevB.63.220507

Exotic superconducting phase in CeCu<inf>2</inf>Si<inf>2</inf> close to antiferromagnetism: A Cu-NQR study under hydrostatic pressure

Y. Kawasaki, K. Ishida, T. Mito, C. Thessieu, G. Zheng, Y. Kitaoka, C. Geibel, F. Steglich

Physical Review B - Condensed Matter and Materials Physics 63 ( 14 ) 1405011 - 1405014 2001年

掲載種別：研究論文（学術雑誌）

We report Cu nuclear-quadrupole-resonance results under pressure (P) on a homogeneous CeCu2Si2 (Tc=0.65 K) that revealed critical magnetic fluctuations at the border to an antiferromagnetic (AF) phase. This exotic superconducting (SC) phase evolves into the typical heavy-fermion SC phase at minute pressures exceeding Pc∼0.2 GPa. The nuclear spin-lattice relaxation data in a P range 0.85 - 2.58 GPa are shown to be accountable by the spin-fluctuation theory based on the nearly AF Fermi-liquid model. In 0≤P< Pc∼0.2 GPa, by contrast, we conclude that the exotic SC phase manifests itself under the unconventional normal state where AF waves propagate over a long range without any trace of AF order and thereby the heavy-fermion state breaks up.

DOI： 10.1103/physrevb.63.140501

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