Faculty Profiles - TEI Kokukei

Papers - TEI Kokukei

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Landau diamagnetism and Weyl-fermion excitations in TaAs revealed by As75 NMR and NQR Reviewed

C. G. Wang, Yoshiaki Honjo, L. X. Zhao, G. F. Chen, K. Matano, R. Zhou, Guo-qing Zheng

Physical Review B 101 ( 24 ) 2020.6

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society (APS)

The electronic and superconducting properties associated with the topologically nontrivial bands in Weyl semimetals have recently attracted much attention. We report the microscopic properties of the type-I Weyl semimetal TaAs measured by As-75 nuclear magnetic (quadrupole) resonance under zero and elevated magnetic fields over a wide temperature range up to 500 K. The magnetic susceptibility measured by the Knight shift K is found to be negative at low magnetic fields and has a strong field (B) dependence as In B at T = 1.56 K. Such nonlinear field-dependent magnetization can be well accounted for by Landau diamagnetism arising from the three-dimensional linearly dispersed bands, and thus is a fingerprint of topological semimetals. We further study the low-energy excitations by the spin-lattice relaxation rate 1/T-1. At zero field and 30 <= T <= 250 K, 1/T1T shows a T-2 variation due to Weyl-node excitations. At B similar to 13 T, 1/T1T exhibits the same T dependence but with a smaller value, scaling with K-2 alpha T-2, which indicates that the Korringa relation also holds for a Weyl semimetal. Analysis of the Korringa ratio reveals that the energy range of the linear bands is about 250 K in TaAs.

DOI： 10.1103/physrevb.101.241110

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.101.241110/fulltext

NMR and NQR studies on transition-metal arsenide superconductors LaRu2As2, KCa2Fe4As4F2, and A(2)Cr(3)As(3) Reviewed

Jun Luo, Chunguang Wang, Zhicheng Wang, Qi Guo, Jie Yang, Rui Zhou, K. Matano, T. Oguchi, Zhian Ren, Guanghan Cao, Guo-Qing Zheng

CHINESE PHYSICS B 29 ( 6 ) 2020.6

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We report As-75-nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements on transition-metal arsenides LaRu2As (2), KCa2Fe4As4F2, and A(2)Cr(3)As(3). In the superconducting state of LaRu2As2, a Hebel-Slichter coherence peak is found in the temperature dependence of the spin-lattice relaxation rate 1/T-1 just below T-c, which indicates that LaRu2As2 is a full-gap superperconducor. For KCa2Fe4As4F2, antiferromagnetic spin fluctuations are observed in the normal state. We further find that the anisotropy rate RAF=T1c/T1ab<i is small and temperature independent, implying that the low energy spin fluctuations are isotropic in spin space. Our results indicate that KCa2Fe4As4F2 is a moderately overdoped iron-arsenide high-temperature superconductor with a stoichiometric composition. For A(2)Cr(3)As(3) (A = Na, K, Rb, Cs), we calculate the electric field gradient by first-principle method and assign the As-75-NQR peaks to two crystallographically different As sites, paving the way for further NMR investigation.

DOI： 10.1088/1674-1056/ab892d

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Direction and symmetry transition of the vector order parameter in topological superconductors CuxBi2Se3 Reviewed

T. Kawai, C. G. Wang, Y. Kandori, Y. Honoki, K. Matano, T. Kambe, Guo-qing Zheng

Nature Communications 11 ( 1 ) 235 2020.1

Authorship：Last author,　Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：NATURE PUBLISHING GROUP

Topological superconductors have attracted wide-spreading interests for the bright application perspectives to quantum computing. Cu0.3Bi2Se3 is a rare bulk topological superconductor with an odd-parity wave function, but the details of the vector order parameter d and its pinning mechanism are still unclear. Here, we succeed in growing CuxBi2Se3 single crystals with unprecedented high doping levels. For samples with x = 0.28, 0.36 and 0.37 with similar carrier density as evidenced by the Knight shift, the in-plane upper critical field H-c2 shows a two-fold symmetry. However, the angle at which the H-c2 becomes minimal is different by 90 degrees among them, which indicates that the d-vector direction is different for each crystal likely due to a different local environment. The carrier density for x = 0.46 and 0.54 increases substantially compared to x <= 0.37. Surprisingly, the in-plane H-c2 anisotropy disappears, indicating that the gap symmetry undergoes a transition from nematic to isotropic (possibly chiral) as carrier increases.

DOI： 10.1038/s41467-019-14126-w

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Tuning the Distance to a Possible Ferromagnetic Quantum Critical Point in A2Cr3As3 Reviewed

J. Luo, J. Yang, R. Zhou, Q. G. Mu, T. Liu, Z.-a. Ren, C. J. Yi, Y. G. Shi, Guo-qing Zheng

Phys. Rev. Lett. 123 047001(1) - 047001(6) 2019.7

NMR studies on noncentrosymmetric superconductor TaRh₂B₂

Ogura Ryo, Matano Kazuaki, Kawasaki Shinji, Zheng Guo-qing

Meeting Abstracts of the Physical Society of Japan 74.2 1987 - 1987 2019

Single Crystal Growth and Characterization of Cu_xBi₂Se₃ II

Kandori Y., Kawai T., Honoki Y., Matano K., Kambe T., Zheng G. -q.

Meeting Abstracts of the Physical Society of Japan 74.2 1074 - 1074 2019

Structural phase transition, antiferromagnetism and two superconducting domes in LaFeAsO1-xFx (0 < x ≤ 0.75) Reviewed

Jie Yang, Toshihide Oka, Zheng Li, HuaiXin Yang, JianQi Li, GenFu Chen, Guo-Qing Zheng

Science China Physics, Mechanics & Astronomy 61 ( 11 ) 2018.11

銅酸化物高温超伝導体における擬ギャップと磁場誘起電荷密度波―Bi2Sr2－x Lax CuO6＋δの場合― Invited Reviewed

川崎慎司, 鄭国慶

日本物理学会誌 73 ( 8 ) 558 - 563 2018.8

Electron Mass Enhancement near a Nematic Quantum Critical Point in NaFe1–xCoxAs Reviewed

C. G. Wang, Z. Li, J. Yang, L. Y. Xing, G. Y. Dai, X. C. Wang, C. Q. Jin, R. Zhou, Guo-qing Zheng

Phys. Rev. Lett. 121 167004 2018.6

Fully gapped spin-singlet superconductivity in noncentrosymmetricPbTaSe2:Pb207nuclear magnetic resonance study Reviewed

S. Maeda, K. Matano, Guo-qing Zheng

Physical Review B 97 ( 18 ) 184510 2018.5

Authorship：Corresponding author Language：English Publishing type：Research paper (scientific journal) Publisher：American Physical Society (APS)

We report the Pb-207 nuclear magnetic resonance (NMR) measurements on polycrystalline sample of PbTaSe2 with noncentrosymmetric crystal structure and topological electronic band. The nuclear spin-lattice relaxation rate 1 / T-1) shows a suppressed coherence peak below the superconducting transition temperature T-c = 4.05 K and decreases as an exponential function of temperature. The penetration depth derived from the NMR spectrum is almost temperature independent below T = 0.7 T-c. The Knight shift K decreases below T-c. These results suggest spin-singlet superconductivity with a fully opened gap 2 Delta = 3.5 k(B)T(c) in PbTaSe2.

DOI： 10.1103/physrevb.97.184510

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Other Link： http://harvest.aps.org/v2/journals/articles/10.1103/PhysRevB.97.184510/fulltext

Nuclear magnetic resonance measurement station in SECUF using hybrid superconducting magnets Reviewed

Zheng Li, Guo-qing Zheng

Chin. Phys. B 27 ( 7 ) 077401 2018

Structural phase transition, precursory electronic anomaly, and strong-coupling superconductivity in quasi-skutterudite (Sr1−xCax)3Ir4Sn13 and Ca3Rh4Sn13 Reviewed

Jun Luo, Jie Yang, S Maeda, Zheng Li, Guo-Qing Zheng

Chin. Phys. B 27 077401 2018

Observation of dopant sites in Cu-doped Bi₂Se₃ topological superconductor by Circularly-Polarized-Light Two-Dimensional Photoelectron Diffraction

Ogi Masafumi, Hashimoto Yusuke, Momono Hiroki, Fukami Shun, Kobayashi Shinta, Peng Dawei, MATANO Kazuaki, Matsuda Hiroyuki, Taguchi Munetaka, Zheng Guo-qing, Daimon Hiroshi

Abstract of annual meeting of the Surface Science of Japan 2018 298 2018

Single crystal growth of Cu_xBi₂Se₃

Kawai T., Honoki Y., Kandori Y., Matano K., Kambe T., Zheng G. -q.

Meeting Abstracts of the Physical Society of Japan 73.1 1332 - 1332 2018

Charge-density-wave order takes over antiferromagnetism in Bi2Sr2−x La x CuO6 superconductors Reviewed

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

Nature Communications 8 ( 1 ) 1267 2017.12

Spin-singlet superconductivity in the doped topological crystalline insulator Sn0.96In0.04Te

Satoki Maeda, Ryohei Hirose, Kazuaki Matano, Mario Novak, Yoichi Ando, Guo-qing Zheng

PHYSICAL REVIEW B 96 ( 10 ) 359 - 384 2017.9

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

The In-doped topological crystalline insulator Sn1-x In-x Te is a candidate for a topological superconductor, where a pseudo-spin-triplet state has been proposed. To clarify the spin symmetry of Sn1-x In-x Te, we perform Te-125-nuclear magnetic resonance (NMR) measurements in polycrystalline samples with 0 <= x <= 0.15. The penetration depth calculated from the NMR line width is T independent below half the superconducting transition temperature (T-c) in polycrystalline Sn0.96In0.04Te, which indicates a fully opened superconducting gap. In this sample, the spin susceptibility measured by the spin Knight shift (K-s) at an external magnetic field of H-mu 0(0) = 0.0872 T decreases below T-c, and K-s(T = 0)/K-s(T = T-c) reaches 0.36 +/- 0.10, which is far below the limiting value 2/3 expected for a spin-triplet state for a cubic crystal structure. Our result indicates that polycrystalline Sn0.96In0.04Te is a spin-singlet superconductor.

DOI： 10.1103/PhysRevB.96.104502

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Gapped Spin-1/2 Spinon Excitations in a New Kagome Quantum Spin Liquid Compound Cu3Zn(OH)(6)FBr

Zili Feng, Zheng Li, Xin Meng, Wei Yi, Yuan Wei, Jun Zhang, Yan-Cheng Wang, Wei Jiang, Zheng Liu, Shiyan Li, Feng Liu, Jianlin Luo, Shiliang Li, Guo-qing Zheng, Zi Yang Meng, Jia-Wei Mei, Youguo Shi

CHINESE PHYSICS LETTERS 34 ( 7 ) 301 - 308 2017.6

Language：English Publishing type：Research paper (scientific journal) Publisher：IOP PUBLISHING LTD

We report a new kagome quantum spin liquid candidate Cu3Zn(OH)(6)FBr, which does not experience any phase transition down to 50 mK, more than three orders lower than the antiferromagnetic Curie-Weiss temperature (similar to 200 K). A clear gap opening at low temperature is observed in the uniform spin susceptibility obtained from F-19 nuclear magnetic resonance measurements. We observe the characteristic magnetic field dependence of the gap as expected for fractionalized spin-1/2 spinon excitations. Our experimental results provide firm evidence for spin fractionalization in a topologically ordered spin system, resembling charge fractionalization in the fractional quantum Hall state.

DOI： 10.1088/0256-307X/34/7/077502

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Systemic Study of Orbital and Spin Nematicity in NaFe1-xCoxAs by NMR

Rui Zhou, Guo-qing Zheng

JOURNAL OF SUPERCONDUCTIVITY AND NOVEL MAGNETISM 30 ( 4 ) 857 - 863 2017.4

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

Nematic order, a self-organized state with rotational symmetry broken, has been observed in both copperoxide and iron-pnictide high temperature superconductors. However, its origin is still a mystery in the iron pnictides although it is considered as a key to understand the mechanism of superconductivity. Here, we report a systemic nuclear magnetic resonance (NMR) study on NaFe(1-x)C(o)xAs (0 <= x <= 0.042) that an orbital order, accompanied by an instant spin nematicity, occurs at at a temperature T* far above structural transition temperature Ts in the tetragonal phase. We show that the observed NMR spectra splitting and its evolution is due to an incommensurate orbital order that sets in below T* and becomes commensurate below T-s. We show that the electric field gradient asymmetry parameter is a good measure for the orbital order parameter which undergoes a Landau-like 2nd-order phase transition. We further show that the spin nematicity is well accounted for by the observed orbital order.

DOI： 10.1007/s10948-017-3997-5

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Quasi-localized Impurity State in Doped Topological Crystalline Insulator Sn0.9In0.1Te Probed by Te-125-NMR

Satoki Maeda, Shota Katsube, Guo-qing Zheng

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 86 ( 2 ) 242 - 249 2017.2

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

The In-doped topological crystalline insulator Sn1-xInxTe is a promising candidate for a topological superconductor, where it is theoretically suggested that In creates an impurity state responsible for superconductivity. We synthesized high purity Sn1-xInxTe samples and performed Te-125-nuclear magnetic resonance (NMR) measurements. The NMR spectra under a magnetic field of H-0 = 5T show a broadening characteristic due to a localized impurity state. The spin-lattice relaxation rate (1/T-1) divided by temperature shows a Curie-Weiss like temperature-dependence under H-0 = 0.1 T but is temperature-independent under H-0 = 5T. These results indicate the existence of quasi-localized impurity states due to In doping.

DOI： 10.7566/JPSJ.86.024702

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Full-gap superconductivity in noncentrosymmetric Re6Zr, Re27Zr5, and Re24Zr5

K. Matano, R. Yatagai, S. Maeda, Guo-qing Zheng

PHYSICAL REVIEW B 94 ( 21 ) 2016.12

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

The noncentrosymmetric superconductor Re6Zr has attracted much interest for its possible unconventional superconducting state with broken time-reversal symmetry. Here we report Re-185/187 nuclear quadrupole resonance measurements on Re6Zr (T-c = 6.72 K) and the isostructural compounds Re27Zr5 (T-c = 6.53 K) and Re24Zr5 (T-c = 5.00 K). The nuclear spin-lattice relaxation rate 1/T-1 shows a coherence peak below T-c and decreases exponentially at low temperatures in all three samples. The superconducting gap Delta derived from the 1/T-1 data is 2 Delta = 3.58k(B)T(c), 3.55k(B)T(c), and 3.51k(B)T(c) for Re6Zr, Re27Zr5, and Re24Zr5, respectively, which is close to the value of 3.53k(B)T(c) expected for weak-coupling superconductivity. These data suggest conventional s-wave superconductivity with a fully opened gap in this series of compounds.

DOI： 10.1103/PhysRevB.94.214513

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