Low-dose radiation effects in thin films of high-temperature superconducting YBa2Cu3O7−x irradiated by 1-MeV electrons

Abstract

Radiation effects are investigated in thin epitaxial films of the high-Tc superconductor (HTSC) YBa2Cu3O7−x irradiated by low doses of 1-MeV electrons. The maximum radiation dose (4×1016 electrons/cm2) is chosen from the condition that the defects formed as a result of electron–nucleus collisions cause a negligible lowering of the critical temperature of YBa2Cu3O7−x. Under this condition the main source of radiation effects in HTSC films can be processes involving excitation of the electronic subsystem of YBa2Cu3O7−x. When YBa2Cu3O7−x films are irradiated by doses of (1–4)×1016 electrons/cm2 their critical temperature Tc is observed to increase (in contrast to published reports of a decrease in Tc at irradiation doses greater than 1018 electrons/cm2) and then, after the irradiation has stopped, to relax over time to its original value. These effects are similar to those observed in the photoexcitation of the electronic subsystem of YBa2Cu3O7−x (photostimulated superconductivity). A decrease of the critical current density in the irradiated YBa2Cu3O7−x films is also observed, which is due to radiation-stimulated changes of the transmissivity to supercurrent of the dislocation walls in low-angle interblock boundaries.