Experiments with d-wave Superconductors

Abstract

The predominant dx2-y2-wave pairing-symmetry of most high-Tc superconductors provides the opportunity to fabricate Josephson junction circuits in which part of the junctions are biased by a phase difference of the superconducting order parameter of π. To explore the road to such π-electronics, we have fabricated and studied all-high-Tc dc superconducting quantum interference devices (dc SQUIDs) realized with thin film technology, of which the Josephson junctions consist of one standard junction and one junction with a π-phase shift. These π-SQUIDs provide clear evidence of the dx2-y2-wave symmetry of the order parameter, the amount of complex admixtures of other symmetry components being undetectably small. This seems to contradict other experiments, the results of which have been presented as evidence for an s-wave order parameter or for complex admixtures. Possible solutions to resolve this apparent contradiction are presented. In particular it is pointed out that even in the bulk of a superconductor the order parameter symmetry (the admixture of various symmetry components) may be spatially dependent.