Temperature and magnetic-field dependence of the conductivity of YBa2Cu3O7−δ films in the vicinity of the superconducting transition: Effect of Tc inhomogeneity

Abstract

Temperature and magnetic field dependences of the conductivity of YBa2Cu3O7−δ films in the transition region are analyzed taking into account spatial inhomogeneity in transition temperature Tc. (i) An expression for the superconducting contribution to conductivity σs(T,H,Tc) of a homogeneous superconductor for low magnetic fields H≪Hc2(0) is obtained using the solution of the Ginzburg-Landau equation in form of perturbation expansions [S. Ullah and A. T. Dorsey, Phys. Rev. B 44, 262 (1991)]. (ii) The error in σs(T,H,Tc) occurring due to the presence of Tc inhomogeneity is calculated and plotted on an H−T plane diagram. These calculations use an effective medium approximation and a Gaussian distribution of Tc. (iii) Measuring the temff mperature dependences of a voltage, induced by a focused electron beam, we determine spatial distributions of the critical temperature for YBa2Cu3O7−δ microbridges with a 2 μm resolution. A typical Tc-distribution dispersion is found to be ≈1K. For such dispersion, error in σs(T,H,Tc) due to Tc inhomogeneity exceeds 30% for magnetic fields H<1T and temperatures |T−Tc|<0.5K. (iv) Experimental R(T,H) dependences of fffresistance are well described by a numerical solution of a set of Kirchoff equations for the resistor network based on the measured spatial distributions of Tc and the expression for σs(T,H,Tc).

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