Andreev spectra and subgap bound states in multiband superconductors.
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.
MESA+ Institute for Nanotechnology, University of Twente, 7500 AE Enschede, The Netherlands.
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Golubov
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A
Brinkman
Yukio
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Tanaka
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Mazin
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Dolgov