Quantum properties of d-wave YBa2Cu3O7-delta Josephson junction

We have measured the transport properties of YBa2CU3O7-delta (YBCO) dc SQUIDs with Josephson junctions characterized by a combination of 45 degrees [001] tilt and alpha [100] tilt grain boundary with alpha = 0 degrees, +/- 10 degrees and 45 degrees. By increasing the component of transport in the YBCO c-axis direction (increasing values of alpha), the SQUIDs showed an enhanced quality factor. At the same time, for all the devices the response under an external magnetic field presented the main features of an unconventional Josephson current phase relation with a pronounced sin 2 phi component. Switching current measurements at low temperature (10th of mK) also revealed that the dynamics of grain boundary junction resulting from a combination of 45 degrees [001] and 45 degrees [100] tilt is dominated by macroscopic quantum tunnelling of the superconductive phase. The features are quite encouraging for applications of cl-wave junctions in quantum circuitry. (c) 2006 Elsevier B.V. All rights reserved.