INFLUENCE OF AN EXTERNAL ELECTRIC-FIELD ON HIGH-T-C SUPERCONDUCTIVITY

The surface superconductivity induced by applying an electric field pe rpendicular to the surface of a high-T-c superconductor covered by an insulator and a gate electrode is studied theoretically. Taking the id ea into account that the change of the surface carrier density confine d in a thin screening layer modulates the transport properties of supe rconductors, we develop a simple method based on the Chen and Yang mod el to study the T-c shift dependence on the applied voltage in the fra meworks of a Thomas-Fermi approximation and BCS theory. In such a case a novel boundary condition is introduced to modify the G-L equations. Solving the modified one, the T-c shift derived by the present model is similar in qualitative behavior to the Shapiro result, but much sim pler in form. In addition, it is shown to be proportional to the appli ed field (the square of applied field) for thin film (thick film) for a given material. Based on our simple results, the critical current de nsity J(c) and nucleation field H-c3 as functions of the applied volta ge are easily derived.