YBCO SQUIDs with unconventional current phase relation

Abstract

We have studied the dynamics of YBa2Cu3O7−δ (YBCO) dc sperconducting quantum interference devices (SQUIDs) characterized by an unconventional Josephson current phase relation (CPR). We have focused on SQUID configurations with Josephson junctions where the lobe of the order parameter in one electrode is facing a node in the other electrode. This order parameter arrangement should enhance the appearance of a sin(2φ) term in the CPR. The response of the critical current of the dc SQUID, under the effect of an external magnetic field, has been measured in temperature, down to 20mK. Our experimental data have been compared with numerical simulations of the SQUIDs dynamics by considering a CPR of a single junction of the form I(φ)=IIsin(φ)−IIIsin(2φ) where II and III are, respectively, the first and second harmonic component. In our devices the values of the sin(2φ) term are such that the fundamental state of the SQUID is naturally double degenerate. This is of great relevance for applications of d-wave SQUIDs in quantum information processing.