Characterization of π-SQUIDs fabricated using orthogonal YBa2Cu3O7.d step edge junctions

Full text: The predominately d-wave nature of the order parameter of high-Tc superconductors offers the possibility to fabricate Josephson junctions (JJ) with a phase shift of π. A dc superconducting quantum interference device (SQUID) in which one JJ is 'normal' and the other is a π-JJ (called a it-SQUID) is expected to demonstrate spontaneous flux generation and a spontaneous persistent current at zero applied field. Under these conditions a π-SQUID needs no external bias and has an intrinsic double-well potential, making it a possible candidate for a qubit in quantum computing. For symmetric π-SQUIDs with a small inductance, the phase shift across the Aπ-junctions causes a minimum in the /C(B) pattern at zero applied field, in contrast to the maximum observed in normal SQUIDs. We outline the design and fabrication of π-SQUIDs using orthogonal step-edge junctions and characterize the devices in terms of expected π-SQUID behaviour. We will also discuss issues relating to experiments performed in a true zero-field environment and overcoming remanent fields that cause trapped flux during the cool down of the device past its critical temperature. Copyright (2005) Australian Institute of Physics