Electric field distribution at low-angle grain boundaries in high-temperature superconductors

Abstract

Electric fields $\mathbf{E}$ are created in type-II superconductors by thermally activated flux creep or flux flow, driven by electric currents through the specimen. Usually, an average value $〈E〉=V/L$ is determined in resistive four-terminal-transport measurements by measuring the voltage V between two contacts with distance L as a function of the applied current. However, this average value can deviate by orders of magnitude of the true local value $\mathbf{E}(x,y),$ if inhomogeneities like grain boundaries are present in the specimen. In this article, we show the spatial distribution of $\mathbf{E}(x,y)$ of high-temperature superconducting bicrystalline films with a low-angle grain boundary in the flux-creep state. Even in a somewhat ``relaxed state,'' the electric-field value in bicrystalline samples varies by about two orders of magnitude.