Faculty Profiles - TEI Kokukei

Papers - TEI Kokukei

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Effects of high magnetic fields on the pseudogap and d-wave superconductivity in the underdoped and overdoped high-T-c superconductors

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

PHYSICA C 341 819 - 822 2000.11

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

Based on measurements of the (CU)-C-63 Knight shift and the nuclear spin-lattice relaxation rate under magnetic fields up to 28 T, we find that the pseudogap in the slightly overdoped TISr2CaCu2O6.88 (T-c=68 K) is due to Cooper pair density fluctuations. Such fluctuations are also found in the underdoped YBa2Cu4O8 (T-c=74 K), but are small and only survive up to T-sf similar or equal to T-c+15K=90 K, which is much lower than the held-independent pseudogap temperature T* similar or equal to 160 K. The implication on the phase diagram is discussed. At low temperatures in the superconducting state, a field-induced finite density of states was found in both compounds and is interpreted as due to the quasiparticles outside a vortex core in a d-wave superconductor.

DOI： 10.1016/S0921-4534(00)00703-6

Superconducting fluctuations and the pseudogap in the slightly overdoped high-Tc superconductor TlSr2CaCu2O6.8: high magnetic field NMR studies

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

Physical Review Letters 85 ( 2 ) 405 - 408 2000.7

Language：English Publishing type：Research paper (scientific journal) Publisher：American Inst of Physics

Measurements in the slightly overdoped superconductor TlSr2CaCu2O6.8 at both zero magnetic field and high fields up to 28 T were made. It was found that the reduction of the Knight shift and 1/T1T above Tc is strongly field dependent and follows a simple scaling relation. Overall, the results indicate that an electron correlation-driven pseudogap would terminate at some doping level before entering the overdoped regime.

DOI： 10.1103/PhysRevLett.85.405

Superconducting fluctuations and the pseudogap in the slightly overdoped high-T-c superconductor TlSr2CaCu2O6.8: High magnetic field NMR studies

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

PHYSICAL REVIEW LETTERS 85 ( 2 ) 405 - 408 2000.7

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

From measurements of the Cu-63 Knight shift (K) and the nuclear spin-lattice relaxation rate (1/T-l) under magnetic fields from zero up to 28 T in the slightly overdoped high-T-c. superconductor TlSr2CaCu2O6.8 (T-c = 68 K), we find that the pseudogap behavior, i.e., the reductions of 1/TlT and K above T-c from the values expected from the normal state at high T, is strongly field dependent and follows a scaling relation. We show that this scaling is consistent with the effects of the Cooper pair density fluctuations. The present finding contrasts sharply with the pseudogap property reported previously in the underdoped regime where no field effect was seen up to 23.2 T. The implications are discussed.

DOI： 10.1103/PhysRevLett.85.405

d-wave vortex and pseudogap in underdoped high-T-c, cuprate YBa2Cu4O8: high-magnetic-field NMR

GQ Zheng, WG Clark, Y Kitaoka, K Asayama, Y Kodama, P Kuhns, WG Moulton

PHYSICA B 281 901 - 903 2000.6

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

The responses to the magnetic field (H) of the superconductivity and the pseudogap in the underdoped high- T-c cuprate YBa2Cu4O8 (T-c = 74 K) are reported up to 23.2 T based on NMR measurements. For temperatures T less than or equal to 15 K, the Hand T-variation of the Cu-63 nuclear spin-lattice relaxation rate (1/T-1) is 1/T-1 proportional to TH and also the Knight shift increases with increasing H. We interpret our results as evidence for H-induced quasiparticle states that extend from the d-wave vortex centers with an ungapped spectrum. Even though H = 23.2 T reduces T-c by 19 K, no effect is seen on the normal-state pseudogap which persists in the temperature region where the superconductivity is destroyed by the field, suggesting that it is a consequence of strong electron correlations. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)01161-8

Cu-NQR study of magnetism and superconductivity in Ce1+xCu2+ySi2 under pressure

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

HYPERFINE INTERACTIONS 128 ( 1-3 ) 193 - 204 2000

Language：English Publishing type：Research paper (scientific journal) Publisher：BALTZER SCI PUBL BV

In order to investigate magnetic properties in the vicinity of the magnetic to superconducting (SC) phase boundary, we have performed Cu-NQR measurements under hydrostatic pressure (P) on two off-stoichiometric Ce1+xCu2+ySi2 polycrystals: Ce0.99Cu2.02Si2 (denoted as Ce 0.99) exhibits the anomalous ground state so-called A phase dominated by critical magnetic correlations and Ce0.975Cu2Si2 (Ce 0.975) shows a static magnetic ordering at ambient P. With increasing P which enhances the Kondo temperature, the fraction of the A phase becomes markedly suppressed, and the SC fraction increases correspondingly, although T-c stays nearly constant in the measured pressure range, P less than or equal to 14.4 kbar. This shows that the P-induced transition from the A to the SC phases is of a first-order type, without passing through a quantum (T -->0) phase transition. However, no superconductivity has been attained in Ce 0.975 up to 19.4 kbar. It is considered that the P-induced superconductivity is sensitive to the sample quality.

DOI： 10.1023/A:1012635716291

Cu-NQR study of magnetism and superconductivity in Ce1+xCu2+ySi2 under pressure

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

HYPERFINE INTERACTIONS 128 ( 1-3 ) 193 - 204 2000

Language：English Publishing type：Research paper (scientific journal) Publisher：BALTZER SCI PUBL BV

In order to investigate magnetic properties in the vicinity of the magnetic to superconducting (SC) phase boundary, we have performed Cu-NQR measurements under hydrostatic pressure (P) on two off-stoichiometric Ce1+xCu2+ySi2 polycrystals: Ce0.99Cu2.02Si2 (denoted as Ce 0.99) exhibits the anomalous ground state so-called A phase dominated by critical magnetic correlations and Ce0.975Cu2Si2 (Ce 0.975) shows a static magnetic ordering at ambient P. With increasing P which enhances the Kondo temperature, the fraction of the A phase becomes markedly suppressed, and the SC fraction increases correspondingly, although T-c stays nearly constant in the measured pressure range, P less than or equal to 14.4 kbar. This shows that the P-induced transition from the A to the SC phases is of a first-order type, without passing through a quantum (T -->0) phase transition. However, no superconductivity has been attained in Ce 0.975 up to 19.4 kbar. It is considered that the P-induced superconductivity is sensitive to the sample quality.

Nuclear magnetic resonance study of strongly correlated superconductors

K Asayama, Y Kitaoka, GQ Zheng, K Ishida, Y Tokunaga, H Mukuda, T Ohno

APPLIED MAGNETIC RESONANCE 19 ( 3-4 ) 305 - 319 2000

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

This paper introduces nuclear magnetic resonance works in the strongly correlated superconductors: heavy-Fermion, high-T-C superconductors and Sr2RuO4. The analyses strongly support the spin-fluctuation-mediated superconductivity model in a high-T-C superconductor.

DOI： 10.1007/BF03162372

In-NQR study of CeIn3 under pressure

C. Thessieu, K. Ishida, T. Mito, S. C. Kawasaki, Y. Kawasaki, G.-q. Zheng, Y.Kitaoka, Y.Onuki

Physica B 2000

Cu-NQR study of magnetism and superconductivity in Ce1+xCu2+ySi2 under pressure

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

HYPERFINE INTERACTIONS 128 ( 1-3 ) 193 - 204 2000

Language：English Publishing type：Research paper (scientific journal) Publisher：BALTZER SCI PUBL BV

In order to investigate magnetic properties in the vicinity of the magnetic to superconducting (SC) phase boundary, we have performed Cu-NQR measurements under hydrostatic pressure (P) on two off-stoichiometric Ce1+xCu2+ySi2 polycrystals: Ce0.99Cu2.02Si2 (denoted as Ce 0.99) exhibits the anomalous ground state so-called A phase dominated by critical magnetic correlations and Ce0.975Cu2Si2 (Ce 0.975) shows a static magnetic ordering at ambient P. With increasing P which enhances the Kondo temperature, the fraction of the A phase becomes markedly suppressed, and the SC fraction increases correspondingly, although T-c stays nearly constant in the measured pressure range, P less than or equal to 14.4 kbar. This shows that the P-induced transition from the A to the SC phases is of a first-order type, without passing through a quantum (T -->0) phase transition. However, no superconductivity has been attained in Ce 0.975 up to 19.4 kbar. It is considered that the P-induced superconductivity is sensitive to the sample quality.

DOI： 10.1023/A:1012635716291

Nuclear magnetic resonance study of strongly correlated superconductors

K Asayama, Y Kitaoka, GQ Zheng, K Ishida, Y Tokunaga, H Mukuda, T Ohno

APPLIED MAGNETIC RESONANCE 19 ( 3-4 ) 305 - 319 2000

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

This paper introduces nuclear magnetic resonance works in the strongly correlated superconductors: heavy-Fermion, high-T-C superconductors and Sr2RuO4. The analyses strongly support the spin-fluctuation-mediated superconductivity model in a high-T-C superconductor.

DOI： 10.1007/BF03162372

Effects of high magnetic fields on the pseudogap and d-wave superconductivity in the underdoped and overdoped high-Tc superconductors

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

Physica C: Superconductivity and its Applications 341-348 ( 3 ) 819 - 822 2000

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

Based on measurements of the 63Cu Knight shift and the nuclear spin-lattice relaxation rate under magnetic fields up to 28 T, we find that the pseudogap in the slightly overdoped TlSr2CaCu2O6.88 (Tc=68 K) is due to Cooper pair density fluctuations. Such fluctuations are also found in the underdoped YBa2Cu4O8 (Tc=74 K), but are small and only survive up to Tsf ≃ Tc+15K=90 K, which is much lower than the field-independent pseudogap temperature T* ≃ 160 K. The implication on the phase diagram is discussed. At low temperatures in the superconducting state, a field-induced finite density of states was found in both compounds and is interpreted as due to the quasiparticles outside a vortex core in a d-wave superconductor. © 2000 Elsevier Science B.V. All righls reserved.

DOI： 10.1016/S0921-4534(00)00703-6

Pseudogap and superconductivity under high magnetic field in underdoped high-T-c cuprate

GQ Zheng, Y Kitaoka, K Asayama, Y Kodama, WG Clark, P Kuhns, WG Moulton

INTERNATIONAL JOURNAL OF MODERN PHYSICS B 13 ( 29-31 ) 3764 - 3766 1999.12

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

The responses to the magnetic field (H) of the superconductivity and the pseudogap in the underdoped high-T-c cuprate YBa2Cu4O8 (T-c=74 K) are reported up, to 23.2 T based on NMR measurements. Even though H=23.2 T reduces T-c by 19 K, no effect is seen on the normal-state pseudogap, which continues in the temperature region where the superconductivity is destroyed by the field. This suggests that the pseudogap, is a consequence of strong electron correlation effects. I;br temperatures T less than or equal to 15 It, the H- and T-variation of the Cu-63 nuclear spin-lattice relaxation rate (1/T-1) is 1/T-1 proportional to TH and also the Knight shift increases with increasing H. We interpret our results as evidence for H-induced quasiparticle states that extend from the d-wave vortex centers with an ungapped spectrum.

DOI： 10.1142/S021797929900388X

Carrier distribution and superconductivity in multilayer high-T-c cuprates proved by Cu-63 NMR

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

JOURNAL OF LOW TEMPERATURE PHYSICS 117 ( 3-4 ) 473 - 477 1999.11

Language：English Publishing type：Research paper (scientific journal) Publisher：KLUWER ACADEMIC/PLENUM PUBL

The carrier distribution among the inequivalent CuO2 planes in multilayer cuprates is investigated by Cu-63 Knight shift measurement with varying the carrier concentration, delta and the number of CuO2 plane in a unit cell, n. We Sound that 70 (60)% of total carriers are doped selectively into two outer CuO2 planes in n = 3 (4). This indicates resultantly that the inhomogeneity of carrier distribution increases with increasing delta and n in multilayer cuprates.

Responses of the pseudogap and d-wave superconductivity to high magnetic fields in the underdoped high-T-c superconductor YBa2Cu4O8: An NMR study

GQ Zheng, WG Clark, Y Kitaoka, K Asayama, Y Kodama, P Kuhns, WG Moulton

PHYSICAL REVIEW B 60 ( 14 ) R9947 - R9950 1999.10

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

The responses to the magnetic field (H) of the pseudogap and the superconductivity in the underdoped high T-c cuprate YBa2Cu4O8 (T-c=74 K) are reported up to 23.2 T based on NMR measurements. Even though 23.2 T reduces T, by 26%, no effect is seen on the normal-state pseudogap, which persists in the temperature range where the superconductivity is destroyed by the field. For temperatures T less than or equal to 15 K, the spin Knight shift increases with increasing H and also the H and T variation of the Cu-63 nuclear spin-lattice relaxation rate (1/T-1) is 1/T-1 proportional to TH. A possible explanation for this finding is offered as due to the H-induced quasiparticle states that extend from the d-wave vortex centers with ungapped spectrum. [S0163-1829(99)50438-4].

DOI： 10.1103/PhysRevB.60.R9947

NMR study of magnetic excitations and pseudogap in HgBa2Ca3Cu4Oy

Y Tokunaga, K Ishida, K Magishi, S Ohsugi, GQ Zheng, Y Kitaoka, K Asayama, A Iyo, K Tokiwa, H Ihara

PHYSICA B-CONDENSED MATTER 259-61 571 - 572 1999.1

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

We report systematic Cu-NMR study on HgBa2Ca3Cu4O10+y with T-c = 123 K comprising respective 4-fold and 5-fold two CuO2 planes surrounded by square and pyramidal oxygens. Possible structure and temperature dependence of the normal-state pseudogap have been extracted from the steep decrease of the spin contribution in the Knight shift, K-s below T-K*similar to 220K. By assuming the linear increase of a size of pseudogap between T-K* and T-c with the d(x2-y2) symmetry, the T-dependence of K-s/K-n in both 4- and 5-fold is reproduced below T-K*. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)01066-7

Study of spin-ladder system under pressure

T Mito, K Magishi, S Matsumoto, GQ Zheng, Y Kitaoka, K Asayama, N Motoyama, H Eisaki, S Uchida

PHYSICA B-CONDENSED MATTER 259-61 1042 - 1043 1999.1

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

High-pressure NMR measurements on a single crystal of hole-doped two-leg ladder compound, Sr(2)Ca(12)Cu(24)O(41), have been carried out up to similar to 1.7 GPa. The activated T-dependences of T(1) and Knight shift at 1.7 GPa assured the persistence of the spin gap in this system. (C) 1998 Elsevier Science B.V, AII rights reserved.

NMR study of high-T-c superconductors and related materials

K Ishida, Y Tokunaga, Y Kitaoka, GQ Zheng, K Magishi, H Mukuda, H Tou, T Mito, K Asayama

PHYSICA B-CONDENSED MATTER 259-61 511 - 516 1999.1

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

Recent NMR measurements on high-ir, and related material Sr2RuO4 by the Osaka group are reviewed. The following results are presented: (1) Study of YBa2Cu3O7, + Ni has revealed that the attractive force is spin in origin. (2) Analysis of T-1, T-2 and Knight shift (K) in various high-T-c, materials supports the antiferromagnetic spin-fluctuation mediated superconducting model. (3) Temperatures at which a pseudogap starts to open obtained by 1/T1T, dK/dT, photoemission and resistivity agree with each other in the Bi2Sr2CaCu2O8 + delta system. (4) O-17 Knight shift measurements in the related material Sr2RuO4 suggests that a triplet pairing is realized in this compound as in the heavy-fermion superconductor UPt3. (C) 1999 Published by Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)01015-1

Carrier distribution and superconductivity in multilayered high-Tc cuprates probed by Cu NMR

Y. Tokunaga, H. Kotegawa, K. Ishida, G.-q. Zheng, Y. Kitaoka, K. Tokiwa, A. Iyo, H. Ihara

Journal of Low Temperature Physics 1999

55Mn NQR/NMR studies of the magnetic properties of YMn2 under pressure

Guo-Qing Zheng, K. Nishikido, K. Ohnishi, Y. Kitaoka, K. Asayama, R. Hauser

Physical Review B - Condensed Matter and Materials Physics 59 ( 21 ) 13973 - 13976 1999

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

We report magnetic properties of the antiferromagnet YMn2 as functions of pressure and temperature (T) obtained from the 55Mn spin-lattice relaxation rate and the Knight shift. An energy-band narrowing due to electron correlation is indicated by the Knight shift measurement and the application of pressure is found to enhance the conduction electron bandwidth. In the pressure-induced paramagnetic state, the system undergoes a crossover from an itinerant spin fluctuation (SF) regime at low T to a local SF regime at high T. It is pointed out that this magnetic crossover of SF resembles that of high-temperature superconductors. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevB.59.13973

55Mn NQR/NMR studies of the magnetic properties of YMn2 under pressure

Guo-Qing Zheng, K. Nishikido, K. Ohnishi, Y. Kitaoka, K. Asayama, R. Hauser

Physical Review B - Condensed Matter and Materials Physics 59 ( 21 ) 13973 - 13976 1999

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

We report magnetic properties of the antiferromagnet YMn2 as functions of pressure and temperature (T) obtained from the 55Mn spin-lattice relaxation rate and the Knight shift. An energy-band narrowing due to electron correlation is indicated by the Knight shift measurement and the application of pressure is found to enhance the conduction electron bandwidth. In the pressure-induced paramagnetic state, the system undergoes a crossover from an itinerant spin fluctuation (SF) regime at low T to a local SF regime at high T. It is pointed out that this magnetic crossover of SF resembles that of high-temperature superconductors. © 1999 The American Physical Society.

DOI： 10.1103/PhysRevB.59.13973

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