GINZBURG-LANDAU THEORY OF JOSEPHSON FIELD-EFFECT TRANSISTORS

A theoretical model of high-T-c Josephson field effect transistors (Jo FETs) based on a Ginzburg-Landau free energy expression whose paramete rs are field- and spatially-dependent is developed. This model is used to explain experimental data on JoFETs made by the hole-overdoped Ca- SBCO bicrystal junctions (three terminal devices). The measurements sh owed a large modulation of the critical current as a function of the a pplied voltage due to charge modulation in the bicrystal junction. The experimental data agree with the solutions of the theoretical model. This provides an explanation of the large field effect, based on the s trong suppression of the carrier density near the grain boundary junct ion in the absence of applied field, and the subsequent modulation of the density by the field. (C) 1996 American Institute of Physics.