Effect of the Temperature, External Magnetic Field, and Transport Current on Electrical Properties, Vortex Structure Evolution Processes, and Phase Transitions in Subsystems of Superconducting Grains and “Weak Links” of Granular Two-Level High-Temperature Superconductor YBa2Cu3O7–δ

Abstract

The temperature dependences of the resistivity of granular high-temperature superconductor YBa₂Cu₃O_7–δ ρ(T) are measured at various transverse external magnetic fields 0 ≤ H_ext ≤ 100 Oe in the temperature range from the resistivity onset temperature T_{ρ = 0} to the superconducting transition critical temperature T_c at the transport current density from 50 to 2000 mA/cm². The effect of the external magnetic field and transport current density on the kinetics of phase transitions in both subsystems of granular two-level HTSC (T = T_c2J, T_c1g, T_c) is determined. The feasibility of the topological phase transition, i.e., the Berezinsky–Kosterlitz–Thouless transition, in the Josephson medium at T_c2J < T_BKT < T_c1g “in transport current” is established, and its feasibility conditions are studied.