Andreev spectra and subgap bound states in multiband superconductors

• Published in: Physical review letters Vol. 103; no. 7; p. 077003
• Main Authors: Golubov, A A, Brinkman, A, Tanaka, Yukio, Mazin, I I, Dolgov, O V
• Format: Journal Article
• Language: English
• Published: United States 14.08.2009
• ISSN: 0031-9007
• DOI: 10.1103/physrevlett.103.077003

A theory of Andreev conductance is formulated for junctions involving normal metals (N) and multiband superconductors (S) and applied to the case of superconductors with nodeless extended s(+/-)-wave order parameter symmetry, as possibly realized in the recently discovered ferropnictides. We find qualitative differences from tunneling into s-wave or d-wave superconductors that may help to identify such a state. First, interband interference leads to a suppression of Andreev reflection in the case of a highly transparent N/S interface and to a current deficit in the tunneling regime. Second, surface bound states may appear, both at zero and at nonzero energies.