Impurity-induced states in superconducting heterostructures

Different heterostructures allow the realization of novel electronic states. Exemplary is the case of quasi 1D heterostructures formed by a superconductor and a semiconductor with spin-orbit coupling in which Majorana zero-energy modes can be realized. The presence of disorder can strongly affect these states and, in general, the properties of the heterostructures. We study the effect of a single impurity on the spectrum of superconducting heterostructures. We find that the coupling between the superconductor and the semiconductor can strongly affect the impurity-induced states and may induce additional sub-gap bound states that are not present in isolated superconductors. For the case of quasi 1D superconductor/semiconductor heterostructures we obtain the conditions for which the low-energy impurity-induced bound states appear.