Phase-coherent charge transport in superconducting heterocontacts

Abstract

Motivated by recent tunneling experiments for high-temperature superconductors, we have examined the effect of a near interface pair potential suppression on the corresponding transport characteristics. Our model structure consists of a tunnel junction between a normal injector and a normal conductor-superconductor bilayer with an interface of a finite transmittance. To study conductance spectra of mesoscopic heterostructures, a simple approach to the coherent charge transport through a double-barrier system proposed by B\"uttiker has been generalized to the case of an anisotropic superconducting order parameter. The impact of local fluctuations of the normal interlayer thickness on Andreev bound states, as well as the magnetic-field effect have been studied. Numerical calculations were carried out for s- and d-wave order parameters. The model provides a clear physical understanding of the near zero-bias conductance features in such heterostructures. It is shown that zero- and finite-bias anomalous conductance peaks in oxide superconductors often interpreted in terms of surface bound states associated with d-wave pairing could be also explained within the s-wave scenario. Some criteria to distinguish between two types of the pairing symmetry are proposed.