On the nature of the electric-field effect on YBa2Cu3O7−δ grain boundary junctions employing epitaxial SrTiO3 gate insulators

Abstract

We have fabricated Josephson field-effect transistors based on YBa2Cu3O7−δ bicrystal grain-boundary junctions (GBJs) and epitaxial SrTiO3 films as gate insulators. The SrTiO3 gate insulator shows high products of the breakdown field Ebd and the dielectric constant εr up to Ebdεr=1.3×1010 V/m allowing measurements over a wide range of applied gate electric-field Eg. The critical current Ic of the GBJs is found to depend highly nonlinear on Eg. Remarkably, the measured Ic(Eg) are very similar to the εr(Eg) curves. This strongly suggests that the observed electric-field effect is not due to a field-induced change in carrier concentration but is related to the dielectric properties of the SrTiO3 gate insulator.

Grain boundaries in high-Tcsuperconductors

“…Using a Ginzburg-Landau-based model it was shown that the I c changes observed by Dong and collaborators are consistent with a field-induced change in the carrier density in the Josephson junction (Betouras et al, 1996). As the measured I c changes were found to scale with the field-dependent, nonlinear dielectric constant of the gate insulator ⑀ r , it was proposed that the effects were caused by an assumed giant piezoelectric effect of the epitaxial SrTiO 3 gate layer (Petersen, Takeuchi, et al, 1995;Windt et al, 1999; see also Grupp and Goldman, 1997). As this hypothesis accounts for neither the small values of the field-induced changes of R n nor the proportionality of the I c changes with ⑀ r , it seems more likely that the electric fringe fields arising from charges embedded in the grain boundaries are affected by the gate field-induced change of ⑀ r .…”

Surface energy and magnetocapacitance of superconductors under electric field bias

“…In figure 3 we present the result for the surface critical field (18) versus the external bias (4). We see that the external bias can enhance or decrease the surface critical value depending on the field direction.…”

Structure and Dielectric Behavior of Epitaxially Grown SrTiO3Film between YBa2Cu3O7-δElectrodes

“…The results revealed that the degraded SrTiO 3 layer is very thin and the dielectric constant of the SrTiO 3 film was dominated by that of single-crystal-like SrTiO 3 layer. For most high temperature superconducting devices such as the field effect transistor (FET), [1][2][3][4][5] a highly epitaxial insulation layer sandwiched between superconducting films is necessary. To obtain a large magnitude of the electric field effect in FET's, both a high breakdown electric field E d and a high dielectric constant " r are required for the gate insulator.…”

“…However, even this value is only a half of that of the STO single crystal. The development of STO films with larger dielectric constants is substantial for the future application, 3,[15][16][17] since the seriously depressed " r limits the area of applications of STO thin films.…”