Order parameter phase sensitive experiments and SDJ dc SQUIDs

Spontaneous generation of persistent dc currents is one of the most striking aspects of the physics of superconducting samples in a frustrated geometry, Trapped vortices, however, are also sources of induced persistent circulating dc currents. In practice, usually, it is very difficult to establish which of the two is the real source of the observed persistent circulating de currents and their only presence without additional and, very often, complicated approaches cannot serve as an unambiguous demonstration of frustration in a specific geometry. Recently, spontaneous generation of circulating ac currents in a frustrated geometry has been predicted. Experimentally observed in spatially distributed junctions dc SQUIDs, the effect cannot be reproduced by trapped vortices in the SQUID. Consequently, detection of spontaneous circulating ac currents is a straightforward demonstration of frustration in a given superconducting configuration. For that reason this effect can serve as an excellent tool to be used in order parameter phase sensitive experiments to determine the pairing symmetry of high transition temperature superconductors. (C) 2001 Elsevier Science B.V. All rights reserved.