Spatially resolved observation of supercurrents across grain boundaries in YBaCuO films

Abstract

Spatially resolved resistivity measurements of current transport across individual grain boundaries have been made on superconducting YBa 2Cu3O7. These experiments were done by low-temperature scanning electron microscopy with a resolution of 1 to 2 micrometers, and they show directly the limitation of the critical current density caused by grain boundaries in YBa2Cu3O 7. Furthermore, complex spatial patterns of the current transport across grain boundaries were observed. These patterns reflect self-excited resonances of the grain boundaries and are closely correlated to the unexplained "sub-gap structure" in the current-voltage characteristics of polycrystalline YBa2Cu3O7.