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

Abstract

Abstruct-We report a series of studies of grain boundary (GB) capacitance for YBazCu30,-s (YBCO) films grown on SrTi03 (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 SrTi03. We have also found that GB capacitance per unit area cGB correlates with the resistance-area product R,A. For our own GBs and GBs reported in the literature the data is is consistent with c G p ( R J ) -' . We attribute this to variations in GB barrier properties, which reduce the active area, whilst maintaining locally the transport mechanism as tunneling.

Capacitance measurements on grain boundaries in Y1−xCaxBa2Cu3O7−δ

“…If the inductance of the junction is dominated by the superconducting electrodes, then the value of the inductance can be simply related to the London penetration depth. 16 By plotting the Fiske resonance voltage against the inverse junction width (effectively a dispersion relation for the junction cavity) the junction inductance can be determined from the gradient if the capacitance is known from the hysteresis. Figure 5 shows a plot of data from several undoped junctions from the literature, together with the data obtained from the 30% doped junction.…”

“…Analysis of the data in the high voltage regime produces a reasonable penetration depth of 180 nm for the junction region. 16 The lower voltage regime, however, has an in-creased gradient and does not produce a consistent penetration depth. This is because the dielectric constant of the substrate is extremely large at these reduced voltages (and hence reduced Josephson frequencies) and substrate effects alter the current distribution in the superconducting electrodes increasing both the inductance and capacitance per unit length of the junction [see Fig.…”

“…[8][9][10][11][12][13][14][15][16] In this work we measure the capacitance of a series of thin film Y 1−x Ca x Ba 2 Cu 3 O 7−␦ grain boundaries. Capacitance as a function of doping was determined from hysteresis in the current-voltage characteristics of Josephson junctions fabricated from the thin films.…”

“…It is necessary to ensure that the capacitance measured is that of the grain boundary alone, and that there is not a large parasitic contribution from the SrTiO 3 substrate. 16 It is important to show that the measured hysteresis is neither significantly increased by heating effects 17 (heating can induce hysteresis in junctions that have no capacitance) nor reduced by the effect of the thermal noise 18 (which leads to premature switching into and out of the superconducting state).…”

Frequency analysis of the dielectric constant ofYBa2Cu3O7Josephson junctions fabricated on bicrystalline substrates

“…The influence of the substrate on the dielectric behavior of the barrier has been reported in the literature. 7,8 In order to discard such contribution we have checked that in our working regime a linear relationship between the McCumber parameter ͑␤ C ͒ and the critical current ͑I C ͒ is fulfilled. Specifically, the predicted relationship for both param-…”