The capacitance of grain boundaries in superconducting films with strontium titanate and other substrates

Bicrystal Josephson junctions have been fabricated with coplanar shunt capa citors on a strontium titanate (SrTiO3) substrate in order to investigate t he origin of the junction capacitance. None of the external structures, whi ch varied in length from 5 mu m to 2 mm, appeared to have any effect on the I-V characteristic. However, a correlation was observed between the juncti on resistance and the capacitance obtained from both the hysteresis in the I-V characteristic and the internal junction (Fiske) resonances. This sugge sts that at least at low temperatures the junction capacitance is intrinsic to the grain boundary and the SrTiO3 substrate does not contribute. The co rrelation between the junction resistance and the capacitance is a common f eature of many grain boundaries in high T-c superconductors reported in the literature, artificial or otherwise. (C) 2000 Elsevier Science B.V. All ri ghts reserved.