FIELD EFFECT TRANSISTOR BASED ON A BI-CRYSTAL GRAIN BOUNDARY JOSEPHSON JUNCTION

We have developed a planar field effect device consisting of an artificial grain boundary junction in an Y iBa(2)Cu(3)O(x) (YBCO) microbridge which was covered by a 300 nm amorphous SrTiO3 layer and a 4 mu m wide gate electrode. The layers were grown on an Y-ZrO2 bi-crystal. The current transport through the weak link, connecting the superconducting drain and source electrodes, was regulated by the voltage of the insulated gate. We have studied devices with different misorientaion angles, theta, between the two halves of the bi-crystal. For 45 degrees non-symmetric tilt grain boundaries, we have observed a strong (more than 50%) enhancement of the supercurrent at positive gate voltage and almost no change, or a slight decrease, at negative voltage. A theoretical model of the device is discussed.