The residual resistance in the superconducting region of the Bi2Sr2CaCu2O8 single crystal

In the oxide superconductor Bi2Sr2CaCu2O8 the residual resistance tails down into the superconducting region below the critical temperature; this is promoted by a magnetic field. For melt-grown single crystals the behaviour is measured and analysed on the basis of the theory of Ambegaokar and Halperin. Two parameters, superconducting transition temperature and current through the spontaneously formed Josephson junction, are assigned to fit the measurements to the theory. The origin of the residual resistance is explained quantitatively by thermal fluctuation. The dependence on the magnetic field is interpreted as the external magnetic field reducing the area of the Josephson junction, introducing a normal conducting area as vortex lines. (author)