Phase Diagrams of Thin Disordered Films Based on HTSC YBa2Cu3O7 – x in External Magnetic Fields

Abstract

An unusual decrease in the slope of the upper critical field near T_c0 at a gradual increase in the ion implantation dose has been experimentally observed in narrow bridges formed on the base of thin HTSC YBa₂Cu₃O_7 – x films, while an increase in the defect concentration usually leads to an increase in the local slope of the phase transition line H_c2(T). In addition, it has been found that the temperature dependence of the upper critical field has a positive curvature near T_c0. A possible theoretical interpretation of the results is proposed. It is based on the modified Ginzburg–Landau theory with a nonuniform length of superconducting correlations.