Faculty Profiles - TEI Kokukei

Papers - TEI Kokukei

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Influence on superconductivity in the parity mixing superconductor Li2T3B(T:Pt,Pd) by non-magnetic impurity and defect doping

G. Bao, Y. Inada, G. Eguchi, Y. Maeno, M. Ichioka, G. -Q. Zheng

PHYSICA C-SUPERCONDUCTIVITY AND ITS APPLICATIONS 494 95 - 98 2013.11

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

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

溶液酸素NMRによる酸化修飾タンパク質の新規検出方法 Reviewed

藤原範子, 花島慎弥, 山口芳樹, 鄭国慶, 鳥越秀峰, 谷口直之, 鈴木敬一郎

日本生化学会大会プログラム・講演要旨集 86回 1P - 104 2013.9

NMR and NQR Studies on Non-centrosymmetric Superconductors Re7B3, LaBiPt, and BiPd

Kazuaki Matano, Satoki Maeda, Hiroki Sawaoka, Yuji Muro, Toshiro Takabatake, Bhanu Joshi, Srinivasan Ramakrishnan, Kenji Kawashima, Jun Akimitsu, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 ( 8 ) 84711-1-84711-5 2013.8

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

We report the nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements for non-centrosymmetric superconductors Re7B3, LaBiPt, and BiPd containing heavy elements. For all three compounds, the spin-lattice relaxation rate 1/T-1 shows a coherence peak just below T-c and decreases exponentially at low temperatures, which indicates that an isotropic superconducting gap is dominant in these compounds. In BiPd, the height of the coherence peak just below T-c is much suppressed, which suggests that there exists a substantial component of gap with nodes in this compound. Our results indicate that heavy element is not the only factor, but the extent of inversion symmetry breaking is also important to induce a large spin-orbit coupling and an unconventional superconducting state.

DOI： 10.7566/JPSJ.82.084711

Quantum criticality in electron-doped BaFe2-xNixAs2

R. Zhou, Z. Li, J. Yang, D. L. Sun, C. T. Lin, Guo-qing Zheng

NATURE COMMUNICATIONS 4 2265-1-2265-7 2013.8

Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

A quantum critical point is a point in a system's phase diagram at which an order is completely suppressed at absolute zero temperature (T). The presence of a quantum critical point manifests itself in the finite-T physical properties, and often gives rise to new states of matter. Superconductivity in the cuprates and in heavy fermion materials is believed by many to be mediated by fluctuations associated with a quantum critical point. In the recently discovered iron-pnictide superconductors, we report transport and NMR measurements on BaFe2 - xNixAs2 (0 <= x <= 0.17). We find two critical points at x(c1) = 0.10 and x(c2) = 0.14. The electrical resistivity follows rho = rho(0) + AT(n), with n = 1 around x(c1) and another minimal n = 1.1 at x(c2). By NMR measurements, we identity x(c1) to be a magnetic quantum critical point and suggest that x(c2) is a new type of quantum critical point associated with a nematic structural phase transition. Our results suggest that the superconductivity in carrier-doped pnictides is closely linked to the quantum criticality.

DOI： 10.1038/ncomms3265

Superconductivity in Tetragonal LaPt2-xGe2+x

Satoki Maeda, Kazuaki Matano, Hiroki Sawaoka, Yoshihiko Inada, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 ( 6 ) 65002-1-65002-2 2013.6

Phonon anomaly and anisotropic superconducting gap in noncentrosymmetric Li-2(Pd1-xPtx)(3)B

G. Eguchi, D. C. Peets, M. Kriener, S. Yonezawa, G. Bao, S. Harada, Y. Inada, G. -q. Zheng, Y. Maeno

PHYSICAL REVIEW B 87 ( 16 ) 161203(R)-1-161203(R)-4 2013.4

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

The Mott State and Superconductivity in Face-Centred Cubic Structured Cs3C60: A Cs-133-Nuclear Magnetic Resonance Study under Pressure

Shinji Kawasaki, Junji Fukui, Takeshi Motoyama, Yuta Suzuki, Seiji Shibasaki, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 82 ( 1 ) 14709-1-14719-6 2013.1

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

Over the past 20 years, fullerides have been studied as the source of high-transition-temperature (T-c) superconductivity except for copper oxides. The recent finding of the Mott insulating state right beside superconductivity in Cs3C60 has suggested that magnetism helps raise T-c even in fullerides as in heavy-fermion compounds, high-T-c copper oxides, two-dimensional organic conductors, and iron pnictides. Namely, one tends to think that the link between Mott insulator and superconductivity takes place in fullerides, which can give rise to the mechanism beyond the Bardeen-Cooper-Schrieffer framework. However, the relationship between the Mott state and the superconductivity in Cs3C60 is still under debate. By nuclear magnetic resonance measurements under pressure, we find that the magnetism and superconductivity in Cs3C60 are competing orders. Different from previous reports, the phase separation of Cs3C60 crystals into the Mott and metallic states allows us to systematically study the evolution of the ground state under pressure. Our careful experiments have found that the prevention of a magnetic order is rather essential for the superconductivity in face-centred cubic Cs3C60, which presents a basic strategy for finding still higher T-c in this system.

DOI： 10.7566/JPSJ.82.014709

A solution O-17-NMR approach for observing an oxidized cysteine residue in Cu,Zn-superoxide dismutase

Shinya Hanashima, Noriko Fujiwara, Kana Matsumoto, Noriyuki Iwasaki, Guo-qing Zheng, Hidetaka Torigoe, Keiichiro Suzuki, Naoyuki Taniguchi, Yoshiki Yamaguchi

CHEMICAL COMMUNICATIONS 49 ( 14 ) 1449 - 1451 2013

Language：English Publishing type：Research paper (scientific journal) Publisher：ROYAL SOC CHEMISTRY

Solution O-17-NMR application to biological macromolecules is extremely limited. We describe here O-17-NMR observation of the O-17(2)-oxidized cysteine side chain of human Cu,Zn-superoxide dismutase in solution using selective O-17(2) oxidation. O-17-NMR with the aid of O-17-labeling has wide potential to probe the environment and dynamics of oxidizable functionalities in proteins.

DOI： 10.1039/c2cc36918d

NMR study of the impurity effects in noncentrosymmetric superconductors Li-2(Pd,Pt)(3)B Reviewed

K. Arima, K. Matano, S. Harada, G. Z. Bao, Y. Inada, G. Q. Zheng

10th International Conference on Materials and Mechanisms of Superconductivity (M2S-X) 449 012034-1 - 012034-3 2013

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

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

Microscopic coexistence of antiferromagnetism and superconductivity in hole-doped Iron-pnictides Ba0.77K0.23Fe2As2 revealed by NMR Reviewed

R. Zhou, Z. Li, J. Yang, G. Q. Zheng

Hyperfine Interactions 222 ( 1-3 ) 95 - 102 2013

Language：English Publishing type：Research paper (scientific journal)

We have performed nuclear magnetic resonance (NMR) measurements on an underdoped single-crystal Ba0. 77K0. 23Fe2As2 with Tc = 16. 5 K. Below TN = 46 K, an internal magnetic field splits the NMR peaks of H ∥ c and shifts those of H ∥ a to higher frequencies. The nuclear spin-lattice relaxation rate 1/T1 measured at the central peak with H ∥ a shows a distinct decrease below Tc(μ0H = 12 T) = 16 K. Our results clearly show that antiferromagnetic order and superconductivity coexist at a microscopical length scale. © 2013 Springer Science+Business Media Dordrecht.

DOI： 10.1007/s10751-013-0862-1

Microscopic coexistence of antiferromagnetic order and superconductivity in Ba0.77K0.23Fe2As2 Reviewed

Z. Li, R. Zhou, Y. Liu, D. L. Sun, J. Yang, C. T. Lin, Guo-qing Zheng

PHYSICAL REVIEW B 86 ( 18 ) 2012.11

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

We report As-75 nuclear magnetic resonance studies on an underdoped single-crystal Ba0.77K0.23Fe2As2 with T-c = 16.5 K. Below T-N = 46 K, the NMR peaks for H parallel to c split and those for H parallel to a shift to higher frequencies, which indicates that an internal magnetic field along the c axis develops below T-N. The spin-lattice relaxation rate 1/T-1 measured at the shifted peak with H parallel to a, which experiences the internal field, shows a distinct decrease below T-c(mu H-0 = 12 T) = 16 K, following a T-3 relation at low temperatures. Our results show unambiguously that antiferromagnetic order and superconductivity coexist microscopically. The unusual superconducting state with the coexisting magnetism is highlighted.

DOI： 10.1103/PhysRevB.86.180501

Pseudogap Ground State and Its Doping Evolution in Bi2Sr2-xLaxCuO6+delta: Removing the Superconducting State by the Application of Very High Magnetic Fields Reviewed

Guo-qing Zheng, S. Kawasaki, C. T. Lin, P. L. Kuhns, A. P. Reyes

JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 25 ( 5 ) 1249 - 1253 2012.7

Language：English Publishing type：Research paper (scientific journal) Publisher：SPRINGER

We present results for the pseudogap ground state and its doping evolution in single-layered copper-oxide Bi2Sr2-x La (x) CuO6+delta . We apply very high magnetic fields up to 44 T to remove the superconducting state and reveal the hidden low temperature (T) normal state. Through Cu-63-NMR Knight shift and spin-lattice relaxation rate measurements, we find that there remains a finite density of states (DOS) at the Fermi level in the zero-T limit when the superconductivity is removed, which indicates that the pseudogap ground state is a metallic state with a finite volume of Fermi surface. The residual DOS in the pseudogap ground state decreases with decreasing doping (increasing x), but remains quite large even at the vicinity of the magnetically ordered phase of xa parts per thousand yen 0.8. The result indicates that the superconductivity emerges from the remaining Fermi surface and coexists with the pseudogap.

DOI： 10.1007/s10948-012-1575-4

MULTIPLE SUPERCONDUCTING GAPS, ANISOTROPIC SPIN FLUCTUATIONS AND SPIN-ORBIT COUPLING IN IRON-PNICTIDES Reviewed

Jie Yang, Guo-Qing Zheng

MODERN PHYSICS LETTERS B 26 ( 15 ) 2012.6

Language：English Publishing type：Research paper (scientific journal) Publisher：WORLD SCIENTIFIC PUBL CO PTE LTD

This article reviews the NMR and NQR studies on iron-based high-temperature superconductors by the IOP/Okayama group. It was found that the electron pairs in the superconducting state are in the spin-singlet state with multiple fully-opened energy gaps. The antiferromagnetic spin fluctuations in the normal state are found to be closely correlated with the superconductivity. Also, the antiferromagnetic spin fluctuations are anisotropic in the spin space, which is different from the case in copper oxide superconductors. This anisotropy originates from the spin-orbit coupling and is an important reflection of the multiple-bands nature of this new class of superconductors.

DOI： 10.1142/S0217984912300086

Luttinger-volume violating Fermi liquid in the pseudogap phase of the cuprate superconductors Reviewed

Jia-Wei Mei, Shinji Kawasaki, Guo-Qing Zheng, Zheng-Yu Weng, Xiao-Gang Wen

PHYSICAL REVIEW B 85 ( 13 ) 134519 2012.4

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

Based on the NMR measurements on Bi2Sr2-xLaxCuO6+delta (La-Bi2201) in strong magnetic fields, we identify the nonsuperconducting pseudogap phase in the cuprates as a Luttinger-volume violating Fermi liquid (LvvFL). This state is a zero-temperature quantum liquid that does not break translational symmetry, and yet, the Fermi surface encloses a volume smaller than the large one given by the Luttinger theorem. The particle number enclosed by the small Fermi surface in the LvvFL equals the doping level p, not the total electron number n(e) = 1 - p. Both the phase string theory and the dopon theory are introduced to describe the LvvFL. For the dopon theory, we can obtain a semiquantitative agreement with the NMR experiments.

DOI： 10.1103/PhysRevB.85.134519

Antiferromagnetic Spin Fluctuations above the Dome-Shaped and Full-Gap Superconducting States of LaFeAsO1-xFx Revealed by As-75-Nuclear Quadrupole Resonance Reviewed

T. Oka, Z. Li, S. Kawasaki, G. F. Chen, N. L. Wang, Guo-qing Zheng

PHYSICAL REVIEW LETTERS 108 ( 4 ) 047001-1-047001-5 2012.1

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

We report a systematic study by As-75 nuclear-quadrupole resonance in LaFeAsO1-xFx. The antiferro-magnetic spin fluctuation found above the magnetic ordering temperature T-N = 58 K for x = 0.03 persists in the regime 0.04 <= x <= 0.08, where superconductivity sets in. A dome-shaped x dependence of the superconducting transition temperature T-c is found, with the highest T-c = 27 K at x = 0.06, which is realized under significant antiferromagnetic spin fluctuation. With increasing x further, the antiferromagnetic spin fluctuation decreases, and so does T-c. These features resemble closely the cuprates La2-xSrxCuO4. In x = 0.06, the spin-lattice relaxation rate (1/T-1) below T-c decreases exponentially down to 0.13T(c), which unambiguously indicates that the energy gaps are fully opened. The temperature variation of 1/T1 below T-c is rendered nonexponential for other x by impurity scattering.

DOI： 10.1103/PhysRevLett.108.047001

Cu-NMR Study of Bi2Sr1.6La0.4CuO6+delta Superconductor in Very High Magnetic Fields Reviewed

S. Kawasaki, C. T. Lin, P. L. Kuhns, A. P. Reyes, Guo-qing Zheng

26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

We report the results of (63,65) Cu-NMR measurements on single-layered copper-oxide Bi2Sr1.6La0.4CuO6+delta (T-c = 32 K) conducted under very high magnetic fields up to 45 T. The high magnetic field suppresses superconductivity completely, and the pseudogap ground state is revealed. The Cu-63-NMR Knight shift shows that there remains a finite density of states at the Fermi level in the zero-temperature limit, which indicates that the pseudogap ground state is a metallic state with a fi nite volume of Fermi surface.

DOI： 10.1088/1742-6596/400/2/022052

Non-magnetic impurity and defect doping in superconductors Li2Pd3B with noncentrosymmetric crystal structures Reviewed

G. Bao, Y. Inada, S. Harada, G-q Zheng

INTERNATIONAL CONFERENCE ON STRONGLY CORRELATED ELECTRON SYSTEMS (SCES 2011) 391 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

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

Spin-orbit coupling, anisotropic magnetic fluctuations and nodeless energy gap in iron-pnictides revealed by NMR Reviewed

Z. Li, J. Yang, Guo-qing Zheng

26TH INTERNATIONAL CONFERENCE ON LOW TEMPERATURE PHYSICS (LT26), PTS 1-5 400 2012

Language：English Publishing type：Research paper (international conference proceedings) Publisher：IOP PUBLISHING LTD

We report on the pairing symmetry and the spin correlations in the Fe(Ni)-based superconductors RFe(Ni)AsO1-xFx (R=Pr, La), LiFeAs and Ba1-xKxFe2As2 single crystals, based on our extensive nuclear magnetic resonance and nuclear quadrupole resonance measurements. The spin susceptibility measured by the Knight shift decreases below T-c along all crystal directions, which indicates spin-singlet pairing. Evidence for multiple gaps is given. We find that the antiferromagnetic spin fluctuation is anisotropic in the spin space due to spin-orbit coupling, but becomes isotropic in the temperature limit, which points to spin-singlet superconductivity with nodeless gap.

DOI： 10.1088/1742-6596/400/2/022145

Magnetic phase diagram of Li-2(Pd1-xPtx)(3)B by ac susceptometry

D. C. Peets, G. Eguchi, M. Kriener, S. Harada, Sk. Md. Shamsuzzamen, Y. Inada, G. -Q. Zheng, Y. Maeno

PHYSICAL REVIEW B 84 ( 5 ) 054521-1-054521-5 2011.8

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

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.84.054521

As-NMR/NQR study of CaFe2As2 under pressure Reviewed

Shinji Kawasaki, Toshihide Oka, Takahisa Tabuchi, X. F. Wang, X. H. Chen, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 80 2011.7

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

As-75-zero-field nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements are performed on CaFe2As2 under pressure. At P = 4.7 and 10.8 kbar, the temperature dependence of nuclear-spin-lattice relaxation rate (1/T-1) measured at tetragonal phase show no coherence peak just below T-c and decrease with decreasing temperature. The superconductivity is of gapless at P = 4.7 kbar but evolves to multiple gaps at P = 10.8 kbar. We find that the superconductivity appears near a quantum critical point. Both electron correlation and superconductivity disappear in the collapsed tetragonal phase. A systematic study under pressure indicates that electron correlations play a vital role in forming Cooper pairs in this compound.

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