Subharmonic gap structure in d-wave superconductors

We present a self-consistent theory of current-voltage characteristics of d-wave/d-wave contacts at arbitrary transparency. In particular, we address the open problem of the observation of subharmonic gap structure (SGS) in cuprate junctions. Our analysis shows that (i) the SGS is possible in d-wave superconductors; (ii) the existence of bound states within the gap results in an even-odd effect in the SGS; (iii) elastic scattering mechanisms, like impurities or surface roughness, may suppress the SGS; and (iv) in the presence of a magnetic field the Doppler shift of the Andreev bound states leads to a splitting of the SGS, which is an unambiguous fingerprint of d-wave superconductivity.