研究者詳細 - 笠原　成

論文 - 笠原　成

分割表示 162 件中 81 - 100 件目／全件表示 >>

21aBA-5 Critical Current Density and Flux Pinning Mechanism of FeSe Single Crystal

Sun Y., Pyon S., Tamegai T., Kobayashi R., Watashige T., Kasahara S., Matsuda Y., Shibauchi T., Kitamura H.

日本物理学会講演概要集 70 1938 - 1938 2015年

Evidence for Time-Reversal Symmetry Breaking of the Superconducting State near Twin-Boundary Interfaces in FeSe Revealed by Scanning Tunneling Spectroscopy

Watashige, T., Tsutsumi, Y., Hanaguri, T., Kohsaka, Y., Kasahara, S., Furusaki, A., Sigrist, M., Meingast, C., Wolf, T., v Loehneysen, H., Shibauchi, T., Matsuda, Y.

Physical Review X 5 ( 3 ) 2015年

掲載種別：研究論文（学術雑誌）

Junctions and interfaces consisting of unconventional superconductors provide<br />
an excellent experimental playground to study exotic phenomena related to the<br />
phase of the order parameter. Not only the complex structure of unconventional<br />
order parameters have an impact on the Josephson effects, but also may<br />
profoundly alter the quasi-particle excitation spectrum near a junction. Here,<br />
by using spectroscopic-imaging scanning tunneling microscopy, we visualize the<br />
spatial evolution of the local density of states (LDOS) near twin boundaries<br />
(TBs) of the nodal superconductor FeSe. The $\pi/2$ rotation of the<br />
crystallographic orientation across the TB twists the structure of the<br />
unconventional order parameter, which may, in principle, bring about a<br />
zero-energy LDOS peak at the TB. The LDOS at the TB observed in our study, in<br />
contrast, does not exhibit any signature of a zero-energy peak and an apparent<br />
gap amplitude remains finite all the way across the TB. The low-energy<br />
quasiparticle excitations associated with the gap nodes are affected by the TB<br />
over a distance more than an order of magnitude larger than the coherence<br />
length $\xi_{ab}$. The modification of the low-energy states is even more<br />
prominent in the region between two neighboring TBs separated by a distance<br />
$\approx7\xi_{ab}$. In this region the spectral weight near the Fermi level<br />
($\approx\pm$0.2~meV) due to the nodal quasiparticle spectrum is almost<br />
completely removed. These behaviors suggest that the TB induces a fully-gapped<br />
state, invoking a possible twist of the order parameter structure which breaks<br />
time-reversal symmetry.

DOI： 10.1103/PhysRevX.5.031022

Anomalous critical fields in quantum critical superconductors 査読

C. Putzke, P. Walmsley, J. D. Fletcher, L. Malone, D. Vignolles, C. Proust, S. Badoux, P. See, H. E. Beere, D. A. Ritchie, S. Kasahara, Y. Mizukami, T. Shibauchi, Y. Matsuda, A. Carrington

NATURE COMMUNICATIONS 5 2014年12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：NATURE PUBLISHING GROUP

Fluctuations around an antiferromagnetic quantum critical point (QCP) are believed to lead to unconventional superconductivity and in some cases to high-temperature superconductivity. However, the exact mechanism by which this occurs remains poorly understood. The iron-pnictide superconductor BaFe2(As1-xPx)(2) is perhaps the clearest example to date of a high-temperature quantum critical superconductor, and so it is a particularly suitable system to study how the quantum critical fluctuations affect the superconducting state. Here we show that the proximity of the QCP yields unexpected anomalies in the superconducting critical fields. We find that both the lower and upper critical fields do not follow the behaviour, predicted by conventional theory, resulting from the observed mass enhancement near the QCP. Our results imply that the energy of superconducting vortices is enhanced, possibly due to a microscopic mixing of antiferromagnetism and superconductivity, suggesting that a highly unusual vortex state is realized in quantum critical superconductors.

DOI： 10.1038/ncomms6679

Anisotropy of the superconducting gap in the iron-based superconductor BaFe2(As1-xPx)(2) 査読

T. Yoshida, S. Ideta, T. Shimojima, W. Malaeb, K. Shinada, H. Suzuki, I. Nishi, A. Fujimori, K. Ishizaka, S. Shin, Y. Nakashima, H. Anzai, M. Arita, A. Ino, H. Namatame, M. Taniguchi, H. Kumigashira, K. Ono, S. Kasahara, T. Shibauchi, T. Terashima, Y. Matsuda, M. Nakajima, S. Uchida, Y. Tomioka, T. Ito, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, H. Ikeda, R. Arita, T. Saito, S. Onari, H. Kontani

SCIENTIFIC REPORTS 4 7292 2014年12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：NATURE PUBLISHING GROUP

We report peculiar momentum-dependent anisotropy in the superconducting gap observed by angle-resolved photoemission spectroscopy in BaFe2(As1-xPx)(2) (x = 0.30, T-c = 30 K). Strongly anisotropic gap has been found only in the electron Fermi surface while the gap on the entire hole Fermi surfaces are nearly isotropic. These results are inconsistent with horizontal nodes but are consistent with modified s(+/-) gap with nodal loops. We have shown that the complicated gap modulation can be theoretically reproduced by considering both spin and orbital fluctuations.

DOI： 10.1038/srep07292

Disorder-induced topological change of the superconducting gap structure in iron pnictides 査読

Y. Mizukami, M. Konczykowski, Y. Kawamoto, S. Kurata, S. Kasahara, K. Hashimoto, V. Mishra, A. Kreisel, Y. Wang, P. J. Hirschfeld, Y. Matsuda, T. Shibauchi

NATURE COMMUNICATIONS 5 5657 2014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：NATURE PUBLISHING GROUP

In superconductors with unconventional pairing mechanisms, the energy gap in the excitation spectrum often has nodes, which allow quasiparticle excitations at low energies. In many cases, such as in d-wave cuprate superconductors, the position and topology of nodes are imposed by the symmetry, and thus the presence of gapless excitations is protected against disorder. Here we report on the observation of distinct changes in the gap structure of ironpnictide superconductors with increasing impurity scattering. By the successive introduction of nonmagnetic point defects into BaFe2(As1 - P-x(x))(2) crystals via electron irradiation, we find from the low-temperature penetration depth measurements that the nodal state changes to a nodeless state with fully gapped excitations. Moreover, under further irradiation the gapped state evolves into another gapless state, providing bulk evidence of unconventional sign-changing s-wave superconductivity. This demonstrates that the topology of the superconducting gap can be controlled by disorder, which is a strikingly unique feature of iron pnictides.

DOI： 10.1038/ncomms6657

Anomalous Fermi surface in FeSe seen by Shubnikov-de Haas oscillation measurements 査読

Taichi Terashima, Naoki Kikugawa, Andhika Kiswandhi, Eun-Sang Choi, James S. Brooks, Shigeru Kasahara, Tatsuya Watashige, Hiroaki Ikeda, Takasada Shibauchi, Yuji Matsuda, Thomas Wolf, Anna E. Boehmer, Frederic Hardy, Christoph Meingast, Hilbert von Loehneysen, Michi-To Suzuki, Ryotaro Arita, Shinya Uji

PHYSICAL REVIEW B 90 ( 14 ) 1 - 144517 2014年10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 have observed Shubnikov-de Haas oscillations in FeSe. The Fermi surface deviates significantly from predictions of band-structure calculations and most likely consists of one electron and one hole thin cylinder. The carrier density is in the order of 0.01 carriers/Fe, an order of magnitude smaller than predicted. Effective Fermi energies as small as 3.6 meV are estimated. These findings call for elaborate theoretical investigations incorporating both electronic correlations and orbital ordering.

DOI： 10.1103/PhysRevB.90.144517

Superconducting gap structure of BaFe_2(As_{1-x}P_{x})_2

L. Malone, Y. Mizukami, P. Walmsley, C. Putzke, S. Kasahara, T. Shibauchi, Y. Matsuda, A. Carrington

2014年9月

掲載種別：研究論文（学術雑誌）

We present a study of the superconducting gap structure in the iron-pnictide<br />
series BaFe2(As1-xPx)2. By measuring the variation of the specific heat as a<br />
function of temperature and magnetic field we are able to determine the number<br />
and Fermi surface location of the nodes in the superconducting gap. In<br />
particular, from measurements of the variation of the specific heat as the<br />
magnetic field is rotated in the ab plane of the sample we conclude that the<br />
nodes are in the [110] directions. Then from a quantitative analysis of the<br />
temperature and field dependence of the specific heat we further conclude that<br />
nodes exists on all Fermi surface sheets.

Infrared pseudogap in cuprate and pnictide high-temperature superconductors 査読

S. J. Moon, Y. S. Lee, A. A. Schafgans, A. V. Chubukov, S. Kasahara, T. Shibauchi, T. Terashima, Y. Matsuda, M. A. Tanatar, R. Prozorov, A. Thaler, P. C. Canfield, S. L. Bud'ko, A. S. Sefat, D. Mandrus, K. Segawa, Y. Ando, D. N. Basov

PHYSICAL REVIEW B 90 ( 1 ) 2014年7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 investigate infrared manifestations of the pseudogap in the prototypical cuprate and pnictide superconductors, YBa2Cu3Oy and BaFe2As2 (Ba122) systems. We find remarkable similarities between the spectroscopic features attributable to the pseudogap in these two classes of superconductors. The hallmarks of the pseudogap state in both systems include a weak absorption feature at about 500 cm(-1) followed by a featureless continuum between 500 and 1500 cm(-1) in the conductivity data and a significant suppression in the scattering rate below 700-900 cm(-1). The latter result allows us to identify the energy scale associated with the pseudogap Delta PG. We find that in the Ba122-based materials the superconductivity-induced changes of the infrared spectra occur in the frequency region below 100-200 cm(-1), which is much lower than the energy scale of the pseudogap. We performed theoretical analysis of the scattering rate data of the two compounds using the same model, which accounts for the effects of the pseudogap and electron-boson coupling. We find that the scattering rate suppression in Ba122-based compounds below Delta PG is solely due to the pseudogap formation, whereas the impact of the electron-boson coupling effects is limited to lower frequencies. The magnetic resonance modes used as inputs in our modeling are found to evolve with the development of the pseudogap, suggesting an intimate correlation between the pseudogap and magnetism.

DOI： 10.1103/PhysRevB.90.014503

Direct observation of lattice symmetry breaking at the hidden-order transition in URu2Si2 査読

S. Tonegawa, S. Kasahara, T. Fukuda, K. Sugimoto, N. Yasuda, Y. Tsuruhara, D. Watanabe, Y. Mizukami, Y. Haga, T. D. Matsuda, E. Yamamoto, Y. Onuki, H. Ikeda, Y. Matsuda, T. Shibauchi

NATURE COMMUNICATIONS 5 4188 2014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：NATURE PUBLISHING GROUP

Since the 1985 discovery of the phase transition at T-HO = 17.5 K in the heavy-fermion metal URu2Si2, neither symmetry change in the crystal structure nor large magnetic moment that can account for the entropy change has been observed, which makes this hidden order enigmatic. Recent high-field experiments have suggested electronic nematicity that breaks fourfold rotational symmetry, but direct evidence has been lacking for its ground state in the absence of magnetic field. Here we report on the observation of lattice symmetry breaking from the fourfold tetragonal to twofold orthorhombic structure by high-resolution synchrotron X-ray diffraction measurements at zero field, which pins down the space symmetry of the order. Small orthorhombic symmetry-breaking distortion sets in at T-HO with a jump, uncovering the weakly first-order nature of the hidden-order transition. This distortion is observed only in ultrapure samples, implying a highly unusual coupling nature between the electronic nematicity and underlying lattice.

DOI： 10.1038/ncomms5188

Doping evolution of the quasiparticle excitations in heavily hole-doped Ba 1 - X K x Fe 2 As 2: A possible superconducting gap with sign-reversal between hole pockets 査読

D. Watanabe, T. Yamashita, Y. Kawamoto, S. Kurata, Y. Mizukami, T. Ohta, S. Kasahara, M. Yamashita, T. Saito, H. Fukazawa, Y. Kohori, S. Ishida, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, A. B. Vorontsov, T. Shibauchi, Y. Matsuda

Physical Review B - Condensed Matter and Materials Physics 89 ( 11 ) 2014年3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：American Physical Society

To gain insight into the unconventional superconductivity of Fe pnictides with no electron pockets, we measure the thermal conductivity κ and penetration depth λ in the heavily hole-doped regime of Ba1-xKxFe2As2. The residual thermal conductivity (κ/T)T→0K and T dependence of λ consistently indicate the fully gapped superconductivity at x=0.76 and the (line) nodal superconductivity at higher hole concentrations. The magnitude of κTTc|T→0K and the slope of λ(T) at low temperatures, both of which are determined by the properties of the low-energy excitations, exhibit a highly unusual nonmonotonic x dependence. These results indicate a dramatic change of the nodal characteristics in a narrow doping range. We suggest that the observed x dependence is naturally explained by a doping crossover of the gap function between the s-wave states with and without sign reversal between Γ-centered hole pockets. © 2014 American Physical Society.

DOI： 10.1103/PhysRevB.89.115112

Doping evolution of the quasiparticle excitations in heavily hole-doped Ba1-xKxFe2As2: A possible superconducting gap with sign-reversal between hole pockets 査読

D. Watanabe, T. Yamashita, Y. Kawamoto, S. Kurata, Y. Mizukami, T. Ohta, S. Kasahara, M. Yamashita, T. Saito, H. Fukazawa, Y. Kohori, S. Ishida, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, A. B. Vorontsov, T. Shibauchi, Y. Matsuda

PHYSICAL REVIEW B 89 ( 11 ) 2014年3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

To gain insight into the unconventional superconductivity of Fe pnictides with no electron pockets, we measure the thermal conductivity. and penetration depth. in the heavily hole- doped regime of Ba1- x K x Fe2As2. The residual thermal conductivity (./ T) T. 0 K and T dependence of. consistently indicate the fully gapped superconductivity at x = 0.76 and the ( line) nodal superconductivity at higher hole concentrations. The magnitude of. T Tc| T. 0 K and the slope of.( T) at low temperatures, both of which are determined by the properties of the low- energy excitations, exhibit a highly unusual nonmonotonic x dependence. These results indicate a dramatic change of the nodal characteristics in a narrow doping range. We suggest that the observed x dependence is naturally explained by a doping crossover of the gap function between the s- wave states with and without sign reversal between - centered hole pockets.

DOI： 10.1103/PhysRevB.89.115112

Pseudogap formation above the superconducting dome in iron pnictides 査読

T. Shimojima, T. Sonobe, W. Malaeb, K. Shinada, A. Chainani, S. Shin, T. Yoshida, S. Ideta, A. Fujimori, H. Kumigashira, K. Ono, Y. Nakashima, H. Anzai, M. Arita, A. Ino, H. Namatame, M. Taniguchi, M. Nakajima, S. Uchida, Y. Tomioka, T. Ito, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, K. Ohgushi, S. Kasahara, T. Terashima, H. Ikeda, T. Shibauchi, Y. Matsuda, K. Ishizaka

PHYSICAL REVIEW B 89 ( 4 ) 2014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：AMER PHYSICAL SOC

The nature of the pseudogap (PG) in high transition temperature (high T-c) superconducting cuprates has been a major issue in condensed matter physics. It is still unclear whether the high T-c superconductivity can be universally associated with the PG formation. Here we provide direct evidence of the existence of the PG phase via angle-resolved photoemission spectroscopy in another family of high T-c superconductor, iron pnictides. Our results reveal a composition-dependent PG formation in the multiband electronic structure of BaFe (2)(As1-xPx)(2). The PG develops well above the magnetostructural transition for low x, persists above the nonmagnetic superconducting dome for optimal x, and is destroyed for x similar to 0.6, thus showing a notable similarity with cuprates. In addition, the PG formation is accompanied by inequivalent energy shifts in the zx/yz orbitals of iron atoms, indicative of a peculiar iron orbital ordering which breaks the fourfold rotational symmetry.

DOI： 10.1103/PhysRevB.89.045101

Field-induced superconducting phase of FeSe in the BCS-BEC cross-over 査読

Kasahara, Shigeru, Watashige, Tatsuya, Hanaguri, Tetsuo, Kohsaka, Yuhki, Yamashita, Takuya, Shimoyama, Yusuke, Mizukami, Yuta, Endo, Ryota, Ikeda, Hiroaki, Aoyama, Kazushi, Terashima, Taichi, Uji, Shinya, Wolf, Thomas, von Loehneysen, Hilbert, Shibauchi, Takasada, Matsuda, Yuji

Proceedings of the National Academy of Sciences of the United States of America 111 ( 46 ) 16309 - 16313 2014年

掲載種別：研究論文（学術雑誌）

Fermi systems in the crossover regime between weakly coupled<br />
Bardeen-Cooper-Schrieffer (BCS) and strongly coupled Bose-Einstein-condensate<br />
(BEC) limits are among the most fascinating objects to study the behavior of an<br />
assembly of strongly interacting particles. The physics of this crossover has<br />
been of considerable interest both in the fields of condensed matter and<br />
ultracold atoms. One of the most challenging issue in this regime is the effect<br />
of large spin imbalance on a Fermi system under magnetic fields. Although<br />
several exotic physical properties have been predicted theoretically, the<br />
experimental realization of such an unusual superconducting state has not been<br />
achieved so far. Here we show that pure single crystals of superconducting FeSe<br />
offer the possibility to enter the previously unexplored realm where the three<br />
energies, Fermi energy $\varepsilon_{\rm F}$, superconducting gap $\Delta$ and<br />
Zeeman energy, become comparable. Through the superfluid response, transport,<br />
thermoelectric response, and spectroscopic-imaging scanning tunneling<br />
microscopy, we demonstrate that $\varepsilon_{\rm F}$ of FeSe is extremely<br />
small, with the ratio $\Delta/\varepsilon_{\rm F}\sim1 (\sim0.3)$ in the<br />
electron (hole) band. Moreover, thermal-conductivity measurements give evidence<br />
of a distinct phase line below the upper critical field, where the Zeeman<br />
energy becomes comparable to $\varepsilon_{\rm F}$ and $\Delta$. The<br />
observation of this field-induced phase provides insights into previously<br />
poorly understood aspects of the highly spin-polarized Fermi liquid in the<br />
BCS-BEC crossover regime.

DOI： 10.1073/pnas.1413477111

Quasiparticle Mass Enhancement Close to the Quantum Critical Point in BaFe2(As1-xPx)(2) 査読

P. Walmsley, C. Putzke, L. Malone, I. Guillamon, D. Vignolles, C. Proust, S. Badoux, A. I. Coldea, M. D. Watson, S. Kasahara, Y. Mizukami, T. Shibauchi, Y. Matsuda, A. Carrington

PHYSICAL REVIEW LETTERS 110 ( 25 ) 257002 - 257002 2013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 a combined study of the specific heat and de Haas-van Alphen effect in the iron-pnictide superconductor BaFe2(As1-xPx)(2). Our data when combined with results for the magnetic penetration depth give compelling evidence for the existence of a quantum critical point close to x = 0.30 which affects the majority of the Fermi surface by enhancing the quasiparticle mass. The results show that the sharp peak in the inverse superfluid density seen in this system results from a strong increase in the quasiparticle mass at the quantum critical point.

DOI： 10.1103/PhysRevLett.110.257002

Normal-state spin dynamics in the iron-pnictide superconductors BaFe2(As1-xPx)(2) and Ba(Fe1-xCox)(2)As-2 probed with NMR measurements 査読

Y. Nakai, T. Iye, S. Kitagawa, K. Ishida, S. Kasahara, T. Shibauchi, Y. Matsuda, H. Ikeda, T. Terashima

PHYSICAL REVIEW B 87 ( 17 ) 2013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

The NMR results in iron pnictides BaFe2(As1-xPx)(2) and Ba(Fe1-xCox)(2)As-2 are analyzed based on the self-consistent renormalization (SCR) spin-fluctuation theory. The temperature dependence of the NMR relaxation rate T-1(-1) as well as the electrical resistivity is well reproduced by a SCR model where two-dimensional antiferromagnetic (AF) spin fluctuations are dominant. The successful description of the crossover feature from non-Fermi-liquid to Fermi-liquid behavior strongly suggests that low-lying spin fluctuations in BaFe2(As1-xPx)(2) and Ba(Fe1-xCox)(2)As-2 possess an itinerant AF nature, and that chemical substitution in the two compounds tunes the distance of these systems to an AF quantum critical point. The close relationship between spin fluctuations and superconductivity is discussed compared with the other unconventional superconductors, cuprate and heavy fermion superconductors. In addition, it is suggested that magnetism and lattice instability in these pnictides are strongly linked via orbital degrees of freedom.

DOI： 10.1103/PhysRevB.87.174507

Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe2(As1-xPx)2 査読

S. Demirdiş, Y. Fasano, S. Kasahara, T. Terashima, T. Shibauchi, Y. Matsuda, Marcin Konczykowski, H. Pastoriza, C. J. Van Der Beek

Physical Review B - Condensed Matter and Materials Physics 87 ( 9 ) 2013年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

We present a comprehensive overview of vortex pinning in single crystals of the isovalently substituted iron-based superconductor BaFe2(As 1-xPx)2, a material that qualifies as an archetypical clean superconductor, containing only sparse strong pointlike pins. Widely varying critical current values for nominally similar compositions show that flux pinning is of extrinsic origin. Vortex configurations, imaged using the Bitter decoration method, show less density fluctuations than those previously observed in charge-doped Ba(Fe1-xCox) 2As2 single crystals. Analysis reveals that the pinning force and energy distributions depend on the P content x. However, they are always much narrower than in Ba(Fe1-xCox) 2As2, a result that is attributed to the weaker temperature dependence of the superfluid density on approaching Tc in BaFe2(As1-xPx)2. Critical current density measurements and pinning force distributions independently yield a mean distance between effective pinning centers L̄∼90 nm, increasing with increasing P content x. This evolution can be understood as being the consequence of the P dependence of the London penetration depth. Further salient features are a wide vortex free "Meissner belt", observed at the edge of overdoped crystals, and characteristic chainlike vortex arrangements, observed at all levels of P substitution. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.87.094506

Interplane resistivity of isovalent doped BaFe2(As 1-xPx)2 査読

M. A. Tanatar, K. Hashimoto, S. Kasahara, T. Shibauchi, Y. Matsuda, R. Prozorov

Physical Review B - Condensed Matter and Materials Physics 87 ( 10 ) 2013年3月

記述言語：英語掲載種別：研究論文（学術雑誌）

Temperature-dependent interplane resistivity ρc(T) was measured for the iron-based superconductor BaFe2(As 1-xPx)2 over a broad isoelectron phosphorus substitution range from x=0 to x=0.60, from nonsuperconducting parent compound to heavily overdoped superconducting composition with Tc≈10K. The features due to structural and magnetic transitions are clearly resolved in ρc(T) of the underdoped crystals. A characteristic maximum in ρc(T), found in the parent BaFe2As2 at around 200 K, moves rapidly with phosphorus substitution to high temperatures. At the optimal doping, the interplane resistivity shows T-linear temperature dependence without any crossover anomalies, similar to the previously reported in-plane resistivity. This observation is in stark contrast with dissimilar temperature dependencies found at optimal doping in electron-doped Ba(Fe 1-xCox)2As2. Our finding suggests that despite similar values of the resistivity and its anisotropy, the temperature-dependent transport in the normal state is very different in electron and isoelectron-doped compounds. Similar temperature dependence of both in-plane and interplane resistivities, in which the dominant contributions are coming from different parts of the Fermi surface, suggests that scattering is the same on the whole Fermi surface. Since magnetic fluctuations are expected to be much stronger on the quasinested sheets, this observation may point to the importance of the interorbital scattering between different sheets. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.87.104506

Interplane resistivity of isovalent doped BaFe2(As1-xPx)(2) 査読

M. A. Tanatar, K. Hashimoto, S. Kasahara, T. Shibauchi, Y. Matsuda, R. Prozorov

PHYSICAL REVIEW B 87 ( 10 ) 2013年3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

Temperature-dependent interplane resistivity rho(c)(T) was measured for the iron-based superconductor BaFe2(As1-xPx)(2) over a broad isoelectron phosphorus substitution range from x = 0 to x = 0.60, from nonsuperconducting parent compound to heavily overdoped superconducting composition with T-c approximate to 10 K. The features due to structural and magnetic transitions are clearly resolved in rho(c)(T) of the underdoped crystals. A characteristic maximum in rho(c)(T), found in the parent BaFe2As2 at around 200 K, moves rapidly with phosphorus substitution to high temperatures. At the optimal doping, the interplane resistivity shows T-linear temperature dependence without any crossover anomalies, similar to the previously reported in-plane resistivity. This observation is in stark contrast with dissimilar temperature dependencies found at optimal doping in electron-doped Ba(Fe1-xCox)(2)As-2. Our finding suggests that despite similar values of the resistivity and its anisotropy, the temperature-dependent transport in the normal state is very different in electron and isoelectron-doped compounds. Similar temperature dependence of both in-plane and interplane resistivities, in which the dominant contributions are coming from different parts of the Fermi surface, suggests that scattering is the same on the whole Fermi surface. Since magnetic fluctuations are expected to be much stronger on the quasinested sheets, this observation may point to the importance of the interorbital scattering between different sheets. DOI: 10.1103/PhysRevB.87.104506

DOI： 10.1103/PhysRevB.87.104506

Disorder, critical currents, and vortex pinning energies in isovalently substituted BaFe2(As1-xPx)(2) 査読

S. Demirdis, Y. Fasano, S. Kasahara, T. Terashima, T. Shibauchi, Y. Matsuda, Marcin Konczykowski, H. Pastoriza, C. J. van der Beek

PHYSICAL REVIEW B 87 ( 9 ) 2013年3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 present a comprehensive overview of vortex pinning in single crystals of the isovalently substituted iron-based superconductor BaFe2(As1-xPx)(2), a material that qualifies as an archetypical clean superconductor, containing only sparse strong pointlike pins [in the sense of C. J. van der Beek et al., Phys. Rev. B 66, 024523 (2002)]. Widely varying critical current values for nominally similar compositions show that flux pinning is of extrinsic origin. Vortex configurations, imaged using the Bitter decoration method, show less density fluctuations than those previously observed in charge-doped Ba(Fe1-xCox)(2)As-2 single crystals. Analysis reveals that the pinning force and energy distributions depend on the P content x. However, they are always much narrower than in Ba(Fe1-xCox)(2)As-2, a result that is attributed to the weaker temperature dependence of the superfluid density on approaching T-c in BaFe2(As1-xPx)(2). Critical current density measurements and pinning force distributions independently yield a mean distance between effective pinning centers (L) over bar similar to 90 nm, increasing with increasing P content x. This evolution can be understood as being the consequence of the P dependence of the London penetration depth. Further salient features are a wide vortex free "Meissner belt", observed at the edge of overdoped crystals, and characteristic chainlike vortex arrangements, observed at all levels of P substitution. DOI: 10.1103/PhysRevB.87.094506

DOI： 10.1103/PhysRevB.87.094506

Importance of both spin and orbital fluctuations in BaFe2(As1-xPx)2 : Evidence from superconducting gap anisotropy 査読

T. Yoshida, S. Ideta, T. Shimojima, W. Malaeb, K. Shinada, H. Suzuki, I. Nishi, A. Fujimori, K. Ishizaka, S. Shin, Y. Nakashima, H. Anzai, M. Arita, A. Ino, H. Namatame, M. Taniguchi, H. Kumigashira, K. Ono, S. Kasahara, T. Shibauchi, T. Terashima, Y. Matsuda, M. Nakajima, S. Uchida, Y. Tomioka, T. Ito, K. Kihou, C. H. Lee, A. Iyo, H. Eisaki, H. Ikeda, R. Arita, T. Saito, S. Onari, H. Kontani

Sci. Rep. 4, 7292 (2014) 2013年1月

掲載種別：研究論文（学術雑誌）

In the iron pnictide superconductors, two distinct unconventional mechanisms<br />
of superconductivity have been put forth: One is mediated by spin fluctuations<br />
leading to the s+- state with sign change of superconducting gap between the<br />
hole and electron bands, and the other is orbital fluctuations which favor the<br />
s++ state without sign reversal. Here we report direct observation of peculiar<br />
momentum-dependent anisotropy in the superconducting gap from angle-resolved<br />
photoemission spectroscopy (ARPES) in BaFe2(As1-xPx)2 (Tc=30 K). The large<br />
anisotropy found only in the electron Fermi surface (FS) and the nearly<br />
isotropic gap on the entire hole FSs are together consistent with modified s+-<br />
gap with nodal loops, which can be theoretically reproduced by considering both<br />
spin and orbital fluctuations whose competition generates the gap modulation.<br />
This indicates that these two fluctuations are nearly equally important to the<br />
high-Tc superconductivity in this system.

　前のページ - 次のページ　

1
2
3
4
5
6
7
8
9