Magnetic Field Dependent Photoinduced Superconductivity and Its Oxygen-Deficient Dependency in Undoped and BZO-doped YBCO Thin Films

Abstract

Abstract We present a systematic study of photoinduced effiect illuminating the undoped and BZO-doped YBCO thin films with laser diode (1.88 eV). The pulsed laser deposited films were post-annealed in partial oxygen pressure in order to decrease the oxygen content and therefore understand the role of structural changes, oxygen ordering and hole doping in photoconductivity phenomenon. The resistivities were measured in the thermally activated flux-flow regime with wide applied magnetic field range. We find that as in undoped and optimally oxygenated YBCO films, the structural defects and dislocations formed by conventional BZO-doping does not contribute to photoinduced enhancement of superconductivity. On the contrary, in our oxygen-deficient films, the effect of photoexcitation is strongly dependent on the oxygen ordering and thereby free-carrier concentration and their mobility in the CuO2 double layers, which again has strong external magnetic field dependence. The magnetic field dependence of the increased superconducting transition shows that the illumination improves the pinning properties in high magnetic field range, indicating the existence of photosensitive pinning centers.