Phase H-T-diagram for MgB₂ granular BCS-superconductor in weak magnetic fields

Abstract

For the purpose of plotting the H-T diagram for MgB₂ granular superconductors, the behavior of electrical resistivity-versus-temperature dependences were studied at ~35 to ~45 K in external magnetic fields with magnetic field strengths Hext up to ~2 kOe. The effect of increasing the superconductivity transition width ΔTc at increased Hext has been revealed. A model has been developed for superconductivity transitions in a two-level system. The data obtained allowed establishing the existence of a weak links system in MgB₂ granular superconductors.