Experimental test for subdominant superconducting phases with complex order parameters in cuprate grain boundary junctions

An experiment to test the formation of subdominant superconducting phases with broken time-reversal symmetry in d-wave superconductors was presented. The variation of the critical current of grain boundary junctions with temperature and magnetic fields was measured to study the formation of a complex order parameter along the surface of YBa₂Cu₃O_7-x films. The onset of a superconducting order parameter was found to affect the magnitude and magnetic field diffraction patterns of the supercurrents.