Kouji Muranaka

Bio: Kouji Muranaka is an academic researcher from Osaka University. The author has an hindex of 1, co-authored 1 publications receiving 10 citations.

Tc-suppression and hole concentration in Cu substituted YBa2(Cu1−xMx)3O7−δ with Fe, Co, Ni, Zn

Abstract: From the studies of the Cu substituted YBa 2 (Cu 1−x M x ) 3 O 7−y (M=Fe, Co, Ni, Zn) systems, it is concluded that the pair-breaking of the Abrikosov and Gor'kov type by magnetic impurities is absent, or very small if it exists, both on the C(1) and Cu(2) sites. The Hall coefficient is measured for the systems. There is a certain relation between T c and n H in the substituted materials with Fe and Co, while no relation is deduced from the Ni- and Zn-substituted ones.

Crystal Structure of Tetragonal YBa_2Cu_ Co_δO_ (δ=0, 0.3)

Abstract: Crystal structures of tetragonal YBa2Cu2.7Co0.3O7-γ and tetragonal YBa2Cu3O7-γ are determined by X-ray and TOF neutron powder diffractometries. Structural parameters are obtained by the Rietveld profile refinement method. In YBa2Cu2.7Co0.3O7-γ', cobalt atoms preferentially occupy one of the copper sites at 1a(0 0 0) rather than the 2g(0 0 z) site with z~0.36. The lattice constants are a = 3.8644(2)A and c = 11.7881(9)A for the quenched YBa2Cu3O6.15 and a = 3.8752(2)A and c = 11.6851(9)A for the furnace-cooled YBa2Cu2.7Co0.3O6.81.

Effect of Ni doping on the thermal expansion of the high- superconductor

Abstract: Thermal expansion measurements have been carried out for the Ni-substituted compounds with a high-resolution dilatometer using the three-terminal capacitance technique. The present set-up is sensitive enough to detect changes in of less than . Results indicate that the jump in the coefficient of linear thermal expansion decreases with increase in Ni content. For x = 1.5%, decreases by a factor of 3 whereas does not change appreciably. There is evidence that the temperature dependence of for compounds with high Ni concentration depends on the conditions of sample growth.

Superconductivity induced phonon anomalies in the Raman spectra of Zn and Ni doped YBa2Cu3O7

Abstract: Here we present Raman spectra of YBa2(Cu1−xZnx)3O7 and YBa2(Cu1−xNix)3O7 as a function of temperature and Zn or Ni content. The temperature dependence of two modes at 340 and 440 cm−1 is analyzed. Similarly to the infrared measurements it is found that Zn substantially suppresses the superconductivity induced phonon softening whereas, Ni does not affect much that effect. Moreover, the superconductivity induced phonon stiffening of the 440 cm−1 mode completely disappeared with the Zn doping. We find this behaviour might support the model where Zn acts effectively as a magnetic pair breaker.

Zn doping effect on point-contact spectra and excess current in Y(Gd)Ba2Cu3O7−δ symmetry of order parameter

Abstract: The considerable changes of the form of the gap singularity in point-contact (PC) spectra and of the temperature dependence of PC spectra and excess current are found when a small increase of Zn content (≈ 1%) in Y(Gd)Ba 2 Cu 3 O 7−δ takes place. The further increase of the Zn content (up to 2.5% in our experiments) changes these characteristics only a little. This observation is more consistent with the prediction of the theory assuming highly anisotropic s wave pairing of carriers.

Magnetic correlations and disorder in a two-dimensional fermi liquid: Possible important effects for high-Tc superconductors

Abstract: The influence of magnetic correlations and disorder in a two-dimensional Fermi liquid is considered in connection with the occurrence of the superconducting state. The disorder effect and magnetic correlations work against the superconducting state but at the same time are competitive phenomena. We show that the critical temperature can decrease due to the magnetic correlations and disorder, but the effect of correlations is reduced by the disorder. The electronic mass enhancement has been calculated taking into consideration the magnetic correlation effects and disorder. Its dependence on the concentration impurities, in agreement with the experimental data, shows the importance of the localization effects due to disorder. These results are in agreement with the experimental data obtained for the high critical temperature superconductors.