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-ς 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 Φ0/2 within ± 3%. This puts limits on the imaginary component of the superconducting order parameter in YBa2Cu3O7-ς.