We are carrying out experiments designed to test for the onset of subdominant superconductor phases induced by scattering from surfaces in d-wave superconductors. Phases with complex order parameters d(x)(2) (2)(-y)+is or d(x)(2) (2)(-y)+id(xy) have been predicted to arise from the suppression of the d-wave order parameter by Andreev reflection from the anisotropic order parameter. We have measured the critical current modulation in grain boundary junctions fabricated from pure and magnetically-doped cuprate films, searching for signatures of a phase transition to a secondary order parameter state. We have also imaged the magnetic field distribution in fabricated superconductor thin films using Scanning SQUID Microscopy, searching for spontaneous circulating currents along the film edges arising from the onset of superconducting phases with broken time-reversal symmetry. Preliminary results show no evidence for complex secondary phases at (100)-surfaces in YBCO. [References: 7]
展开▼
