Theory of charge transport in diffusive normal metal/unconventional superconductor junctions

Novel theory of charge transport which is available for both a diffusive normal metal/unconventional singlet superconductor (DN/USS) and a diffusive normal metal/triplet superconductor (DN/TS) junctions is presented based on the Keldysh–Nambu quasiclassical Green's function formalism. For DN/USS junctions, proximity effect in DN region and the mid gap Andreev resonant state (MARS) formed at the USS side of the DN/USS interface strongly compete each other. On the other hand, for DN/TS junctions, proximity effect is enhanced by the MARS. In DN/TS junction, the total resistance is drastically reduced and is completely independent of the resistance of the DN in the extreme case. We can also check this dramatic effect by numerical simulations without using quasiclassical formalism.