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 YBa2Cu 3O7-delta (YBCO) films grown on SrTiO3 (STO) bicrystal substrates, By varyi ng 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 pro duct R(n)A. For our own GBs and GBs reported in the literature the data is is consistent with c(GB proportional to)(R(n)A)(-1). We attribute this to v ariations in GB barrier properties, which reduce the active area, whilst ma intaining locally the transport mechanism as tunneling.