PROBING THE SYMMETRY OF THE PAIRING STATE OF UNCONVENTIONAL SUPERCONDUCTORS BY SQUID INTERFEROMETER MEASUREMENTS

Phase-sensitive SQUID interferometer experiments have emerged as the m ost powerful technique for determining the symmetry of the pairing sta te of unconventional superconductors. This approach uses Josephson tun neling to probe specific directions in k-space and long-range phase co herence to measure the phase anisotropy of the order parameter, allowi ng a direct and definitive determination of the symmetry. Developed fo r testing the symmetry of the cuprates, corner SQUID and junction expe riments indicate a sign change in the order parameter in orthogonal in -plane directions in YBCO, strong evidence for d(x)2-(y)2 pairing. Now , this technique is being applied to other classes of superconductors suspected to be unconventional.