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