Matsumoto Kaname

Analysis of I-V characteristics in Ag/Bi2223 tapes by weak link path model

When transport current increases in Ag/Bi2223 tapes, the electric field is moderately generated in the vicinity of its critical current (Ic), suggesting that the transition from superconducting (SC) state to non-superconducting (non-SC) state is not sharp. An origin of this behavior is suggested to be a complexity of microscopic current transport, while the transport is dominated by homophase grain boundary weak links. In order to investigate the influence of weak links on I-V characteristics of the tapes, we have proposed a two-dimensional model named Weak Link Path Model. This model consists of SC and non-SC elements linked by weak links with coordination number Z. In the present paper, the influence of Z upon I-V characteristics is clarified. From the numerical analysis based on the model, the following results are obtained; (1) The larger Z is, the higher the Ic is. (2) Large Z lattices have finite (non-zero) Ic even with smaller volume fraction (Vf) of SC phase. Consequently, it is suggested that it ...

Uniaxial Strain Effects on Superconducting Transition in Y0.98Ca0.02Ba2Cu4O8

The effects of uniaxial strain and hydrostatic pressure on Y0.98Ca0.02Ba2Cu4O8 [called Y0.98(Ca0.02)-124] are investigated via AC magnetic measurements under stress corresponding to a pressure of (at most) 20 GPa. Hydrostatic contraction results in the largest enhancement of the superconducting transition temperature (Tc), whose maximum is 99 K, which is slightly lower than the maximum Tc achieved in YBa2Cu4O8 (called Y-124). The Meissner signal disappears at a hydrostatic pressure of approximately 15 GPa. This pressure region representing the Meissner signal is reduced by the out-of-plane contraction (along the c-axis), whereas it is increased by the in-plane contraction (along the c-plane). In the case of Y-124, both uniaxial contractions result in the disappearance of the Meissner signal at approximately 10 GPa prior to reaching the overdoped region. However, by doping Ca into the Y-site, we could investigate uniaxial strain effects characteristic of the so-called 124 structure without causing the stre...