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Experimental Determination of the Pairing State of the High-Temperature Superconductors 

We are probing details of the order parameter in the high-temperature superconductors by Josephson tunneling and SQUID interferometry measurements. Using edge junctions fabricated on cuprate thin films to define the tunneling direction, we can measure both the magnitude and relative phase of the order parameter in arbitrary ab-plane momentum directions. In particular, we are studying SQUIDs with junctions on the (100) and (110) faces of YBCO to test for surface-induced subdominant complex order parameters with broken time-reversal symmetry. We are also studying the effect of the loop inductance on the spontaneously generated magnetic flux in corner SQUIDs incorporating a d-wave superconductor. By varying the inductance in situ by moving a superconducting shield, we can test for the predicted abrupt onset of the spontaneous circulating current at a particular value of the inductance screening parameter.

For more infromation:

D. J. Van Harlingen. "Phase-sensitive tests of the symmetry of the pairing state in the high temperature superconductors --- Evidence for d_x2_-y2 symmetry," Rev. Mod. Phys. 67, 515 (1995). PDF