SYMMETRY-TESTS USING THE HALF-INTEGER FLUX QUANTUM EFFECT IN CUPRATE SUPERCONDUCTING RINGS

The presence or absence of the half-integer flux quantum effect in controlled orientation tricrystal grain boundary rings is a general test of the phase of the superconducting order parameter. One such test proves that this effect is symmetry dependent, and that the order parameter in YBa2Cu3O7-delta has lobes and nodes consistent with d-wave symmetry. Our measurements show that the flux in the 1/2 integer ground state is quantized to Phi(0)/2 within +/-3%. This puts limits on the imaginary component of the superconducting order parameter in YBa2Cu3O7-delta.