Field effect transistor based on a bi-crystal grain boundary Josephson junction

The authors have developed a planar field effect device consisting of an artificial grain boundary junction in an Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub x/ (YBCO) microbridge which was covered by a 300-nm amorphous SrTiO/sub 3/ layer and a 4- mu m-wide gate electrode. The layers were grown on Y-ZrO/sub 2/ bicrystal. The current transport through the weak link, connecting the superconducting drain and source electrodes, was regulated by the voltage of the insulated gate. Devices with different misorientation angles, theta , between the two halves of the bicrystal were studied. For 45 degrees nonsymmetric tilt grain boundaries, the authors 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. At positive gate voltages of 0.5 V and 8 V about 40% and 70% enchancement of the device critical current, respectively, was obtained.<>