Y. Kodama

63Cu NQR/NMR Study of Zn-Substituted YBa2 Cu4 O8 –Effect of Impurity on Spin-Gap-Like Behavior–

The nuclear-spin-lattice relaxation rate, 1/ T 1 , and the Knight shift, K a b , of 63 Cu in the plane have been measured for YBa 2 ( Cu 1- x Zn x ) 4 O 8 ( x =0.01 and 0.02) in order to unravel th...

Tc vs n Relationship for Multilayered High-Tc Superconductors

We have proposed a T c vs n relationship for multilayered high- T c superconductors from the analysis of HgBa 2 Ca n -1 Cu n O y grain-aligned samples containing n =6 to 16 phases. The sample showed a large and sharp superconducting transition at 105 K in its susceptibility vs temperature curve. This means that multilayered HgBa 2 Ca n -1 Cu n O y can maintain a high T c at least up to n ≈16, otherwise many transitions would have been observed. It is generally believed that the highest T c decreases with n for n ≥4–5 for multilayered superconductors. We conclude that the highest T c is almost constant above about n =5 if the factors reducing T c , such as disorder, are eliminated for multilayered superconductors. This behavior can be explained using an inhomogeneous charge distribution model in multilayered cuprates.

Antiferromagnetic Phase Transition in Four-Layered High-Tc, Superconductors Ba2Ca3Cu4O8(FyO1-y)2 with Tc = 55-102 K: 63Cu- and 19F-NMR Studies

We report on the magnetic characteristics of four-layered high- T c superconductors Ba 2 Ca 3 Cu 4 O 8 (F y O 1- y ) 2 with apical fluorine through 63 Cu- and 19 F-NMR measurements. The substitution of oxygen for fluorine at the apical site increases carrier density ( N h ) and T c from 55 up to 102 K. The NMR measurements reveal that antiferromagnetic order, which can uniformly coexist with superconductivity, exists up to N h ≃0.15, which is somewhat smaller than N h ≃0.17, the quantum critical point (QCP) for five-layered compounds. The fact that the QCP for the four-layered compounds moves to a region of lower carrier density than for five-layered ones ensures that a decrease in the number of CuO 2 layers makes an interlayer magnetic coupling weaker.

Simplest nontoxic double-layered cuprate Ba2CaCu2O4(O,F)2 superconductor with a transition temperature of 108K

We report synthesis and properties of the simplest double-layered cuprate superconductor Ba2CaCu2O4(O,F)2. A superconducting transition temperature (Tc) has been achieved as high as 108K for a sample with a nominal fluorine content y=1.6 in Ba2CaCu2O6−yFy. The Tc is the highest among double-layer cuprates that are free of toxic elements such as Hg, Tl, and Pb so that the nontoxic Ba2CaCu2O4(O,F)2 will be promising for application. As y decreases from approximately 2, the a-axis length decreases and the Tc increases from 40to108K. The material is underdoped at large y and as y decreases, the doping moves toward an optimally doped state.

Anomalous behaviour of irreversibility lines in multi-layered superconductor (Cu,C)Ba2Ca3Cu4Oy

The physical properties of a multi-layered cuprate superconductor (Cu0.6C0.4)Ba2Ca3Cu4Oy are investigated using high-quality samples of varying oxygen content (?10.34). Samples are synthesized using a newly developed method capable of fine control of the starting oxygen and carbon compositions, followed by annealing under N2 flow at various temperatures to modify the oxygen content. While Tc, the lattice constants and T0 change monotonically with y, the irreversibility lines exhibit a discontinuous drop at amongst a more gradual decrease. This discontinuity has not been observed before for single-?or double-layered CuO2 superconductors. This anomaly is attributed to the presence of two different order parameters in this material, arising from the large difference in carrier concentrations of the outer five-coordinated CuO2 planes and inner four-coordinated CuO2 planes. The superconducting gap in the outer planes develops with decreasing y (approaching the optimal doping state), suppressing the decrease in the irreversibility line, while the carrier insensitivity of the inner planes limits the change in Tc. Two different kinks are also observed in the irreversibility lines, tentatively attributed to the development of the superconducting gap and 2D?3D crossover in a vortex system. Control of the doping state of both the inner and outer planes is demonstrated to be important in the design of Jc and Birr, even if the change in Tc is small. This result is also expected to be applicable to other multi-layered superconductors.

Disorder-Driven Quantum Phase Transition from Antiferromagnetic Metal to Insulating State in Multilayered High-Tc Cuprate (Cu,C)Ba2Ca4Cu5Oy

We report on superconducting (SC) characteristics for the oxygen-reduced Cu-based five-layered high-temperature superconductor (Cu,C)Ba 2 Ca 4 Cu 5 O y [Cu-1245(OPT)], which includes pyramidal oute...

Electron-doped superconductivity induced by oxygen vacancies in as-grown Sr0.6Ca0.4CuO2?? infinite-layer films

Thin films of the infinite-layer compound Sr0.6Ca0.4CuO2?? have been prepared by off-axis rf magnetron sputtering on SrTiO3 (001). For an optimum level of oxygen vacancy superconductivity was observed (Tc onset = 42 K and Tc(? = 0) = 11 K). Structural and transport data suggesting n-type superconductivity are presented and discussed. Infinite-layer thin films of Sr0.6Ca0.4CuO2??, without trivalent cation doping and showing n-type superconductivity, are reported for the first time.

Irreversibility line and flux pinning properties in a multilayered cuprate superconductor of Ba2Ca3Cu4O8(O,F)2 (Tc = 105 K)

Irreversibility line (IL) and flux pinning properties were investigated for a Ba2Ca3Cu4O8(O,F)2 (F-0234) multilayered cuprate superconductor with a Tc of 105 K. The intragrain critical current density (Jc) and irreversibility field (Birr) were determined by using Beans critical state model for the grain-aligned sample (nominal composition Ba2Ca3Cu4O8.7F1.3). The irreversibility line (IL) of F-0234 is much lower than that of (Cu,C)Ba2Ca3Cu4Oy ((Cu, C)-1234) and HgBa2Ca3Cu4Oy (Hg-1234) in spite of the spacing between the superconducting blocks of F-0234 (7.3 A) being much thinner. The double logarithmic plot of Birr field versus [1−(T/Tc) ] analysis hints that the flux line melting model has been adopted. An anisotropy factor of 65 was calculated from a 3D to 2D crossover field of about 0.95 T. Due to the high anisotropy of this system, a low IL has resulted. The flux pinning force density Fp ( ≈JcB) exhibits scaling behaviour when the magnetic field B is normalized by the Birr field. Analysis of the normalized pinning force reveals that a surface pinning mechanism is dominant and the reduced magnetic field bmax = 0.2 agrees with surface pinning mechanism with closely spaced pins.

Electron-doped superconductivity in Sr1−xCaxCuO2−δ infinite-layer thin films

Abstract Thin films of infinite-layer compound Sr1−xCaxCuO2−δ have been prepared by rf magnetron sputtering. For an optimum level of oxygen vacancy superconductivities were observed ( T c onset =42 and 50 K, T c (ρ=0) =11 and 20 K). Structural and transport data suggest that the doping mechanism is electron-type. The superconducting transitions were also confirmed by ac susceptibility. Further increase of doping showed to destroy superconductivity.

Tc dependence on the number of CuO2 planes in multilayered Ba2Can-1CunO2n(O, F)2 superconductors

Multilayered cuprates of Ba2Can-1CunO2n(O, F)2 (F-02(n-1)n) with n = 5 - 9 have been synthesized by using high pressure synthesis method in order to investigate the variation of Tc. The temperature dependence of susceptibility showed that the Tc (about 80 K) does not depend on n for n = 5 - 9. This result can be explained using the carrier imbalance model in multilayered cuprates. Charge reservoir layers supply most of the carriers to adjacent CuO2 planes (OP) and the OP keeps the Tc constant even for large n.