研究者詳細 - 鄭　国慶

論文 - 鄭　国慶

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Unconventional Superconductivity in Skuterudite Compound PrOs4Sb12

H. Kotegawa, M. Yogi, Y. Imamura, G.-q. Zheng, Y. Kitaoka, S. Ohsaki, H. Sugawara, Y. Aoki, H. Sato

Acta Phys. Polonica B 2003年

Coexistence of antiferromagnetic and paramagnetic electronic phases in quasi-one-dimensional (TMTSF)(2)PF6

AV Kornilov, VM Pudalov, Y Kitaoka, K Ishida, GQ Zheng, T Mito, JS Qualls

JETP LETTERS 78 ( 1 ) 21 - 24 2003年

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 INST PHYSICS

Phase transitions occuring in a quasi-one-dimensional organic compound (TMTSF)(2)PF6 near the boundaries between the paramagnetic metallic (PM), antiferromagnetic insulator (AFI), and superconducting (SC) states were studied experimentally. A controlled transition through the phase boundary was achieved by maintaining the sample at fixed temperature T and pressure P, while the critical pressure was tuned by varying a magnetic field B. When the PM/AFI phase boundary was crossed due to the variation of a magnetic field, history effects were observed: the resistance was found to depend on the trajectory described by the system before arriving at a given point (P-B-T) of the phase space. The results of the experiment give evidence for the formation of a macroscopically inhomogeneous state characterized by the inclusions of a minor phase that is spatially separated from the major phase. Away from the phase boundary, the homogeneous state is restored. After this, upon approaching the phase boundary in the back direction, the system exhibits no features of the minor phase up to the very boundary. (C) 2003 MAIK "Nauka/Interperiodica".

DOI： 10.1134/1.1609570

Gapless magnetic and quasiparticle excitations due to the coexistence of antiferromagnetism and superconductivity in [formula presented]: A study of [formula presented] NQR under pressure 査読

S. Kawasaki, T. Mito, Y. Kawasaki, G. q. Zheng, Y. Kitaoka, D. Aoki, Y. Haga, Y. Ōnuki

Physical Review Letters 91 ( 13 ) 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report systematic measurements of ac susceptibility, nuclear-quadrupole-resonance spectrum, and nuclear-spin-lattice-relaxation time ([Formula presented]) on the pressure ([Formula presented])-induced heavy-fermion superconductor [Formula presented]. The temperature ([Formula presented]) dependence of [Formula presented] at [Formula presented] has revealed that antiferromagnetism (AFM) and superconductivity (SC) coexist microscopically, exhibiting the respective transition at [Formula presented] and [Formula presented]. It is demonstrated that SC does not yield any trace of gap opening in low-lying excitations below [Formula presented], but [Formula presented], followed by a [Formula presented] law. These results point to the unconventional characteristics of SC coexisting with AFM. We highlight that both of the results deserve theoretical work on the gapless nature in the low-lying excitation spectrum due to the coexistence of AFM and SC and the lack of the mean-field regime below [Formula presented]. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevLett.91.137001

Fermi-Liquid Ground State in the [Formula presented]-Type [Formula presented] Copper-Oxide Superconductor 査読

Guo-qing Zheng, T. Sato, Y. Kitaoka, M. Fujita, K. Yamada

Physical Review Letters 90 ( 19 ) 4 2003年

記述言語：英語掲載種別：研究論文（学術雑誌）

We report nuclear magnetic resonance studies on the low-doped [Formula presented]-type copper-oxide [Formula presented] ([Formula presented]) in the superconducting state and in the normal state uncovered by the application of a strong magnetic field. We find that when the superconductivity is removed the underlying ground state is the Fermi liquid state. This result is at variance with that inferred from previous thermal conductivity measurement and appears to contrast with that in [Formula presented]-type copper oxides with a similar doping level where high-[Formula presented] superconductivity sets in within the pseudogap phase. The data in the superconducting state are consistent with the line-node gap model. © 2003 The American Physical Society.

DOI： 10.1103/PhysRevLett.90.197005

¹¹⁵In-NQR evidence for unconventional superconductivity in CeIn<inf>3</inf> under pressure 査読

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

Physical Review B - Condensed Matter and Materials Physics 66 ( 5 ) 545211 - 545214 2002年8月

掲載種別：研究論文（学術雑誌）

We report evidence for unconventional superconductivity in CeIn3 at a pressure P=2.65 GPa above the critical pressure (Pc∼2.5 GPa) revealed by measurements of the nuclear-spin-lattice-relaxation time (T1) and ac susceptibility (ac-x). Both measurements of T1 and ac-x have pointed to a superconducting transition at Tc=95 mK, which is much lower than the onset temperature Tonset=0.15 K at zero resistance. The temperature dependence of 1/T1 shows no coherence peak just below Tc, indicative of an unconventional nature for the superconductivity induced in CeIn3.

Coexistence of antiferromagnetism and superconductivity in heavy-fermion systems

Y Kitaoka, Y Kawasaki, T Mito, S Kawasaki, GQ Zheng, K Ishida, D Aoki, Y Haga, R Settai, Y Onuki, C Geibel, F Steglich

JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS 63 ( 6-8 ) 1141 - 1146 2002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：PERGAMON-ELSEVIER SCIENCE LTD

We report the novel pressure (P)-temperature (T) phase diagrams of antiferromagnetism (AFM) and superconductivity (SC) in CeRhIn5, CeIn3, and CeCu2Si2 revealed by the nuclear quadrupole resonance measurement. In the itinerant helical magnet CeRhIn5, we found that the Neel temperature T-N is reduced at P greater than or equal to 1.23 GPa with an emergent pseudogap behavior. The coexistence of AFM and SC is found in a narrow P range of 1.63-1.75 GPa, followed by the onset of SC with line-node gap over a wide P window 2.1-5 GPa. In CeIn3, the localized magnetic character is robust against the application of pressure up to P similar to 1.9 GPa, 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. In CeCu2Si2, the SC and AFM coexist on a microscopic level once its lattice parameter is expanded. We remark that the underlying marginal AFM state is due to collective magnetic excitations in the superconducting state in CeCu2Si2. An interplay between AFM and SC is discussed on the SO(5) scenario that unifies AFM and SC. We suggest that the SC and AFM in CeCu2Si2 have a common mechanism. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00133-6

Superconducting and magnetic characteristics in the multilayered high-Tc cuprates TlBa2Ca2Cu3O10-y with Tc>130 K probed by Cu and Tl NMR: High value for Tc

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 ) 1845041 - 1845044 2002年5月

記述言語：英語掲載種別：研究論文（学術雑誌）

We report 63Cu and 205Tl nuclear magnetic resonance (NMR) measurements on trilayered high-Tc compounds TlBa2Ca2Cu3O10-y (Tl-1223) that were synthesized at a high pressure and exhibits a high value of superconducting (SC) transition temperature Tc &gt
130 K. In the SC state, the nuclear spin-lattice relaxation rate 1/T1 reveals a T3 behavior below Tc, followed by a T1T=const 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 Nres(EF) is incorporated at the Fermi level to be consistent with the experiments. The important finding is that the size [in Nres (EF)] is much smaller for the present compounds of Tl-1223 with Tc &gt
130 K 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 Tc in Tl-1223 has revealed a value higher than 130 K.

Superconducting and magnetic characteristics in the multilayered high-T-c cuprates TlBa2Ca2Cu3O10-y with T-c > 130 K probed by Cu and Tl NMR: High value for T-c

H Kotegawa, Y Tokunaga, K Ishida, GQ Zheng, Y Kitaoka, A Iyo, Y Tanaka, H Ihara

PHYSICAL REVIEW B 65 ( 18 ) 2002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 Cu-63 and Tl-205 nuclear magnetic resonance (NMR) measurements on trilayered high-T-c compounds TlBa2Ca2Cu3O10-y (Tl-1223) that were synthesized at a high pressure and exhibits a high value of superconducting (SC) transition temperature T-c>130 K. In the SC state, the nuclear spin-lattice relaxation rate 1/T-1 reveals a T-3 behavior below T-c, followed by a T1T=const 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 N-res(E-F) is incorporated at the Fermi level to be consistent with the experiments. The important finding is that the size [in N-res(E-F)] is much smaller for the present compounds of Tl-1223 with T-c>130 K 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 T-c in Tl-1223 has revealed a value higher than 130 K.

DOI： 10.1103/PhysRevB.65.184504

Cu-NQR study of CeCu2(Si0.98Ge0.02)(2) under hydrostatic pressure

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

PHYSICA B-CONDENSED MATTER 312 428 - 430 2002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：ELSEVIER SCIENCE BV

We report a pressure effect on CeCu2(Si0.98Ge0.02)(2) where an anti ferromagnetic order below T-N similar to 0.75 K coexists with superconductivity below T-c similar to0.4 K. At pressures exceeding 0.56 GPa, the magnetic order is suppressed and concomitantly the unconventional superconducting state evolves into a typical heavy-fermion one with a line-node gap. This result demonstrates that the magnetic order is due to the lattice expansion caused by doping Ge. We remark that the characteristic feature of exotic coexisting state at ambient pressure is the persistence of low-lying magnetic excitations even in the superconducting state. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01531-9

Systematic NQR study of the pressure-induced transition from antiferromagnetic to superconducting state in CeRhIn5

Takeshi Mito, Shinji Kawasaki, Guo-Qing Zheng, Yu Kawasaki, Kenji Ishida, Yoshio Kitaoka, Dai Aoki, Yoshinori Haga, Yoshichika Onuki

Physica B: Condensed Matter 312-313 16 - 18 2002年3月

記述言語：英語掲載種別：研究論文（国際会議プロシーディングス）

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 at the In site is substantially reduced from 1.75 kOe at P = 0 to 0.39 kOe at P = 1.23 GPa, while TN slightly changes with increasing P. This suggests that either the size or the direction of the ordered moment changes as P increases. In the SC state at P = 2.1 GPa, the nuclear spin-lattice relaxation rate has revealed a T3 dependence without the coherence peak just below Tc, giving evidence for the unconventional superconductivity. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01157-7

Systematic NQR study of the pressure-induced transition from antiferromagnetic to superconducting state in CeRhIn5

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

PHYSICA B-CONDENSED MATTER 312 16 - 18 2002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：ELSEVIER SCIENCE BV

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 held at the In site is substantially reduced from 1.75 kOe at P = 0 to 0.39 kOe at P = 1.23 GPa, while T-N slightly changes with increasing P. This suggests that either the size or the direction of the ordered moment changes as P increases. In the SC state at P = 2.1 GPa, the nuclear spin-lattice relaxation rate has revealed a T-3 dependence without the coherence peak just below T-c, giving evidence for the unconventional superconductivity. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01157-7

Delocalized quasiparticles in the vortex state of an overdoped high-T-c superconductor probed by Cu-63 NMR

GQ Zheng, H Ozaki, Y Kitaoka, P Kuhns, AP Reyes, WG Moulton

PHYSICAL REVIEW LETTERS 88 ( 7 ) 2002年2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 SOC

We report the spin Knight shift (K-s) and the nuclear spin-lattice relaxation rate (1/T-1) in the vortex state as a function of magnetic field (H) up to 28 T in the high-T-c superconductor TlSr2CaCu2O6.8 (T-c = 68 K). At low temperatures well below T-c, both K-s and 1/T-1 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 d-wave superconductor. The density of states (DOS) around the saddle point is found to be similar tokappaN(o)rootH/H-c2, with kappa = 0.5-0.7 and N-o being the normal-state DOS.

DOI： 10.1103/PhysRevLett.88.077003

Pressure-temperature phase diagram of antiferromagnetism and superconductivity in ceRhIn<inf>5</inf> and CeIn<inf>3</inf>: ¹¹⁵In-NQR study under pressure

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

Physical Review B - Condensed Matter and Materials Physics 65 ( 2 ) 205041 - 205044 2002年1月

掲載種別：研究論文（学術雑誌）

We report the pressure (P)-temperature (T) phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 revealed by the 115In nuclear-spin-lattice-relaxation (T1) measurement. In the itinerant magnet CeRhIn5, we found that the Néel temperature TN is reduced at P ≥ 1.23 GPa with an emergent pseudogap behavior. In CeIn3, the localized magnetic character is robust against the application of pressure up to P ∼ 1.9 GPa, 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.

Evolution of the Magnetism and Superconductivity in CeRhIn5 under Pressure: In-115-NQR Study 査読

Kawasaki Shinji, Mito Takeshi, Zheng Guo-qing, Kawasaki Yu, Ishida Kenji, Kitaoka Yoshio, Aoki Dai, Haga Yoshinori, Onuki Yoshichika

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 282 - 284 2002年1月

記述言語：英語出版者・発行元：Physical Society of Japan

We report a novel pressure(<italic>P</italic>)-induced evolution on the magnetism in the <italic>P</italic>-induced superconductor CeRhIn₅revealed by measurements of the ¹¹⁵In nuclear–spin–lattice-relaxation rate (¹¹⁵1/<italic>T</italic>₁). In the itinerant antiferromagnet CeRhIn₅with the Néel temperature <italic>T</italic>_N=3.8 K at <italic>P</italic>=0, <italic>T</italic>_Nbegins to be reduced to <italic>T</italic>_N=3.6 K at <italic>P</italic>=1.23 GPa that is close to the border of the superconducting phase. An emergent behavior is the observation of a pseudogap behavior that is revealed by a broad peak in the temperature dependence of 1/<italic>T</italic>₁<italic>T</italic>at <italic>P</italic>=1.23 GPa. With further increasing <italic>P</italic>up to <italic>P</italic>=2.1 GPa where its bulk superconductivity is fully established, the pseudogap behavior is not seen in the normal state. The insensitive <italic>P</italic>dependence of <italic>T</italic>_cin CeRhIn₅is suggested to be related to that of the characteristic temperature <italic>T</italic>^*which marks a localized to itinerant magnetic crossover.

DOI： 10.1143/JPSJS.71S.282

Pressure-temperature phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3: In-115-NQR study under pressure

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

PHYSICAL REVIEW B 65 ( 2 ) 2002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

We report the pressure (P)-temperature (T) phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 revealed by the In-115 nuclear-spin-lattice-relaxation (T-1) measurement. In the itinerant magnet CeRhIn5, we found that the Neel temperature T-N is reduced at P greater than or equal to 1.23 GPa with an emergent pseudogap behavior. In CeIn3, the localized magnetic character is robust against the application of pressure up to Psimilar to1.9 GPa, 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.

DOI： 10.1103/PhysRevB.65.020504

Li-7-NMR Study of Spin Liquid State due to Orbital Fluctuation in LiNiO2

Tatsuya Fujimoto, Guo-qing Zheng, Yoshio Kitaoka, Atsushi Hirano, Ryoji Kanno, Mikio Takanu

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 169 - 171 2002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：PHYSICAL SOC JAPAN

We report magnetic field (H) effect on the unconventional magnetism. in LiNiO9 that conSists of a spin-1/2 triangular (TM) lattice through the tLi nuclear spin lattice relaxation (1/T-1) and NMR intensity measurements. Instead of a ferromagnetic (FM) ground state expected from. the FM-Weiss constant, a marginal ordered state emerges below T-M -> 20 K, evidenced from the wipe-out effect of Li-7-NMR signal and the divergent behavior of 1/T-1 towards T-M. The existence of the strong antiferromagnetic (.,NIF) interaction along with the FM one is concluded to lead to a magnetically frustrated state at low temperatures and its AF exchange constant J(AF) is estimated to be about 20 K. This marginal ordered, state due to the frustration of the antiferro-orbital order is found to he suppressed by applying H exceeding 10 T, revealing an orbital exchange constant J(0) similar to -10 K. In the paramagnetic regime at high temperatures, the system behaves like an assembly of local moments with an exchange frequency omega(ex) similar to 11 K. consistent with the energy scale of vertical bar J(0)vertical bar similar to 10 K. The present experiments have revealed that vertical bar J(0)vertical bar similar to 10 K is lower than spin exchange constants J(FM) similar to 30 K vertical bar J(AF)vertical bar similar to 20 K.

DOI： 10.1143/JPSJS.71S.169

Strongly Correlated Metallic State of LaNiO3: La-139 NMR Study

Akihiro Sakai, Guo-qing Zheng, Yoshio Kitaoka

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 166 - 168 2002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：PHYSICAL SOC JAPAN

LaNiO3 is a transition-metal oxide with Perovskite crystal structure where Ni is in the low spin state of r(2g)(6)e(g)(1),. It is a metal and shows enhanced susceptibility x with a strong temperature (T) dependence at low T. We have carried out a La-139 NMR study in the polycrystal sample in the temperature range between 1,4 K and 300 K. We find that the uniform spin susceptibility is T-independent which suggests that the low-T upturn in x is an extrinsic property of the metallic state. The results of the Knight shift and the nuclear spin relaxation rate indicate that the spin susceptibility is almost wave-vector (q) independent, implying that the electron correlation is " dominantly due to a band narrowing, MASS enhancement, effect near a metal-insulator transition, rather than to a ferromagnetic interaction peaked at q=0,

DOI： 10.1143/JPSJS.71S.166

Anisotropic Magnetic Fluctuations and Unconventional Superconductivity in the Layered Heavy Fermion Compound CeIrIn5

Guo-qing Zheng, Kenji Tanabe, Shinji Kawasaki, Yoshio Kitaoka, Dai Aoki, Yoshinori Haga, Yoshichika Onuki

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 71 279 - 281 2002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：PHYSICAL SOC JAPAN

We report the 'In nuclear spin-lattice relaxation rate (1/T-1) measurements down to 90 mK in the new heavy fermion (HF) compound CeIrIn5. At 0.4 K <= T <= 100 K, 1/T-1 is strongly T-dependent, which indicates that the 4f electrons are much more itinerant than in known Ce-based HFs. From the unique temperature variation of 1/T1T, we find that this compound is located near a quantum critical point, with anisotropic spin fluctuations due to a layered crystal structure, Below the hulk superconductivity temperature 0.40 K, 1/T-1, follows a T-3 variation without a coherence peak, which indicates unconventional superconductivity with line-node gap. These aspects are reminiscent of the high-T-c copper oxides and suggest the importance of the magnetic fluctuations for the occurrence of the unconventional superconductivity

DOI： 10.1143/JPSJS.71S.279

115In-NQR evidence for unconventional superconductivity in CeIn3 under pressure.

S. Kawasaki, T. Mito, Y. Kawasaki, G.-q. Zheng, Y. Kitaoka, H. Shishido, S. Araki, R. Settai, Y. Onuki

Phy. Rev. B 2002年

Evolution of antiferromagntism and superconductivity in CeRhIn5 under pressure.

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

J. Phys. Soc. Jpn. 2002年

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