Capacitance as a probe of high angle grain boundary transport in oxide superconductors

We report a series of studies of grain boundary (GB) capacitance for YBa₂Cu₃O_7-δ (YBCO) films grown on SrTiO₃ (STO) bicrystal substrates. By varying the film thickness and the width of the track containing the GB, we find that the substrate makes no contribution to the capacitance measured using Fiske resonances or hysteresis in most cases. This is due to the frequency dependence of the dielectric properties of SrTiO₃. We have also found that GB capacitance per unit area c_GB correlates with the resistance-area product R_nA. For our own GBs and GBs reported in the literature the data is is consistent with c _GB∝(R_nA)^-1. We attribute this to variations in GB barrier properties, which reduce the active area, whilst maintaining locally the transport mechanism as tunneling