CONDUCTANCE ANOMALIES IN A NORMAL-METAL-D-WAVE SUPERCONDUCTOR JUNCTION

The effects of Andreev reflection on the current-voltage characteristi c and differential conductance of a junction between a normal metal an d a d(xy)-wave superconductor, or equivalently, a d(x)2-(y)2-wave supe rconductor with a {110}-oriented surface are investigated using the Bo goliubov-de Gennes equations. Our study elucidates several important c onsequences of the sign change of a d-wave order parameter. In particu lar, a zero-bias conductance peak is obtained when an insulating barri er exists at the interface between the normal metal and the d-wave sup erconductor, consistent with numerous experiments performed on cuprate superconductors. If the insulating barrier is assumed to reside in th e normal metal, several coherence lengths away from the superconductor surface, bound states within the energy gap, and consequent subgap re sonances in the differential conductance, are predicted. The positions of these resonances are out of phase with respect to those predicted for an isotropic or anisotropic s-wave superconductor, thus providing unique signatures of pairing state symmetry.