Dimensional crossover and flux dynamics in low- and high-T c multilayers

Abstract

The temperature and field dependence of the flux creep rate S(T,H)=M0dMJd(lnt) and critical current j(T,H) have been measured in low- Tc (Pb/Ge) and high- Tc (YBa2Cu3O7IPrBa2Cu3O7) (YBCOIPrBCO) multilayers with different coupling strength between the superconducting layers. By taking thicker insulating separator layers, the dimensional crossover from an anisotropic 3D to a quasi 2D behaviour is induced. The detailed analysis of the S(T,H) and j(T,H) dependence made it possible to identify the pinning regimes as predicted by the collective pinning theory. In YBCO/PrBCO multilayers with completely decoupled YBCO planes, a strong enhancement of the quantum flux creep rate S(T—O) has been observed. The value of S(T—O)3% in the 3D YBCO superconductor and increases up to S(T—*O) 2O% in the quasi 2D YBCOIPrBCO multilayers. We also used magnetic fields H<H3D÷2D to decouple the Cu02 planes in Bi2Sr2CaCu2O8 (BSCCO) single crystals. A great similarity between the S(T,H0) andjc(T,Ho) curves has been found in BSCCO, with the superconducting layers decoupled by the applied field, and in the YBCOIPrBCO with the YBCO layers decoupled by inserting thick insulating PrBCO layers.