Electric field controllable Josephson junctions of high quality in high-T c superconductors

Abstract

Three-terminal Josephson junctions, the third terminal of which can be used to control the electronic properties of the device, are the key to a number of exciting device applications of high-Tc superconductors. To this end a novel device structure has been developed, which consists of an inverted metal-insulator-superconductor field-effect transistor into which a bicrystal grain boundary junction is embedded. These devices are excellent Josephson junctions as exemplified by their current–voltage characteristics and the magnetic field dependencies of the critical currents. The critical current of the junctions can be changed by 8% per volt applied to the gate electrode, the gate currents being negligible. Because they are sensitive to electric as well as magnetic fields, the junctions can be controlled by two independent inputs.

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

“…Here, I c ͑solid circles͒ is plotted together with ⑀ r ͑open triangles͒ as a function of E g and V g , respectively. In contrast to other measurements in a smaller range of applied fields, 8 the I c (E g ) dependences of our JoFETs are highly nonlinear. In particular, the slope of the I c (E g ) curves changes sign on going from negative to positive E g as shown in Fig.…”

“…We note, however, that in a limited field range, typically, 0рE g р10 MV/m, we also observe an almost linear I c (E g ) dependence as reported by other groups. 8 Remarkably, the functional dependence I c (E g ) is very close to that of ⑀ r (E g ), i.e., we clearly find a linear relation between the E g -induced changes in I c and ⑀ r . This is demonstrated in the insets of Fig.…”

“…4 For the resulting Josephson field-effect transistor ͑JoFET͒ electricfield-induced changes in I c have been observed in channels with thickness as large as d sd ϭ50, 5 100, 6 and 250 nm. 7 8 However, a detailed understanding of the observed electric-field effects in HTS JoFETs is still lacking. In particular, the scaling of the achievable ⌬I c /I c with the I c R n product or the critical current density J c of the GBJs as well as the absence of any electric-field effect on the normal resistance R n is not understood.…”

Tailoring of high-Tc Josephson junctions by doping their electrodes

“…These fringe fields provide access to measure the properties of the space-charge layers, and to a limited extent are useful to modify the junction properties, for example, by altering the dielectric environment of the junction, as done in field effect experiments. 24 Besides affecting the carrier density, Ca doping is known to decrease the oxygen concentration and to enhance the density of oxygen defects. 19 These effects have to be expected to also occur at interfaces.…”

Influence of a perpendicular magnetic field on the thermal depinning of a single Abrikosov vortex in a superconducting Josephson junction

“…These studies are of interest because Nb junctions are used in a wide range of electronic applications. Such junctions are useful, for instance, in superconducting quantum interference devices (SQUIDS) or in vortex-flow transistors because their performance can be enhanced by tuning the parameters of the individual junctions to optimum operation values [31]. Furthermore gated Josephson junctions can be used as…”