Phase-coherent charge transport in superconducting heterocontacts

Motivated by recent tunneling experiments for high-temperature superconduct ors, we have examined the effect of a near interface pair potential suppres sion on the corresponding transport characteristics. Our model structure co nsists of a tunnel junction between a normal injector and a normal conducto r-superconductor bilayer with an interface of a finite transmittance. To st udy conductance spectra of mesoscopic heterostructures, a simple approach t o the coherent charge transport through a double-barrier system proposed by Buttiker has been generalized to the case of an anisotropic superconductin g order parameter. The impact of local fluctuations of the normal interlaye r thickness on Andreev bound states, as well as the magnetic-field effect h ave 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 superconduc tors often interpreted in terms of surface bound states associated with d-w ave pairing could be also explained within the s-wave scenario. Some criter ia to distinguish between two types of the pairing symmetry are proposed. [ S0163-1829(99)11013-0].