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

Electric fields 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 E(x,y), if inhomogeneities like grain boundaries are present in the specimen. In this article, we show the spatial distribution of 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.