Magnetoresistance of superconducting grains in ceramic YBa2Cu3O7 − δ high-temperature superconductors in weak magnetic fields

Abstract

The current-voltage characteristics \(E(j)_{H_{treat} } = const\) of ceramic (granular) YBa2Cu3O6.95 samples preliminarily magnetized in different transverse magnetic fields Htreat have been measured in a zero field (Hext = 0) at T = 77.3 K for elucidating specific features of dissipation in superconducting grains of high-temperature superconductors (HTSCs). The current-voltage curves measured in the range 0 ≤ Htrap ≤ Hc2J (where Htrap is the magnetic field trapped as a result of the pretreatment in Htreat and Hc2J is the upper critical field of the Josephson weak links) have been used to construct the field dependences of the magnetoresistance ρA(Htreat)j = const of superconducting grains. It has been established that the magnetoresistance ρA of the superconducting grains is significantly lower than the magnetoresistance ρJ for the Josephson medium. The dependence of ρA on Htreat and on the transport current density j has been investigated. It has been shown that the dependences ρA(Htreat)j = const exhibit a clearly pronounced tendency to saturation, ρsatur, and the value of ρsatur increases with increasing j. It has been found that the lower critical field Hc1A of the superconducting grains strongly depends on the transport current density.