Visualization of a Berezinskii–Kosterlitz–Thouless Topological Phase Transition in a Josephson Medium: Detection of an Anomalous Temperature Dependence of the Magnetoresistance of YBa2Cu3O7–δ Granular High-Temperature Superconductors

The possibility of implementing a Berezinskii–Kosterlitz–Thouless topological phase transition in a Josephson medium of two-level high-temperature superconductors induced by a magnetic field has been studied. The effect of temperature and external magnetic field on the transport properties of the YBa 2 Cu 3 O 7–δ granular high-temperature superconductor considered as a model object is studied experimentally. For the first time, an anomalous behavior of the magnetoresistance isotherms is detected in a narrow range of temperature and external magnetic field indicating a topological phase transition in the Josephson medium of granular high-temperature superconductors.