Dissipation and anisotropy in ultrathin YBa_2Cu_3O_7/PrBa_2Cu_3O_7 superlattices

摘要

Ultrathin superlattices of 123 superconducting cuprates have been fabricated by high oxygen pressure sputtering technique. The superlattices show high quality, with negligible step disorder, roughness and interdiffusion. The insulating PrBa_2Cu_3O_7 (PBCO) layer thickness has been kept constant at 5 unit cells (u.c.) and the superconducting YBa_2Cu_3O_7 (YBCO) layer thickness has been changed from 8 u.c. to 1 u.c. In these uncoupled multilayers the critical temperature (T_(c0)) changes from 44 (1 u.c. YBCO) to 80 K (8 u.c. YBCO). In the vortex liquid regime, at constant temperature, the angular dependence of the magnetoresistance scales down with the applied magnetic field values in all the temperature range. This behavior allows us to study the anisotropy and dimensionality behavior of the mixed state in ultrathin superlattices. A dimensional crossover 3D-2D is found in the anisotropy with the 1 u.c. YBCO superlattices following a pure 2D behavior.