Abstract
We have studied the conductance of normal metal-superconductor junctions with a potential barrier on the interface containing localized electron states. The probabilities of the Andreev reflection and the quasiparticle transmission are calculated using a one-dimensional model with a single localized state. The conductance of the junctions with many localized states described by a uniform distribution of the bound state energies around the Fermi level is calculated in the low-temperature region. It is shown that the Andreev reflection processes assisted by the resonant tunneling result in new features of the conductance, such as a zerobias maximum, a low-energy gaplike structure, and a two-gap behavior of the conductance at applied voltages near the value corresponding to the energy gap of the superconductor. The current-voltage characteristics for high applied voltages reveal both an excess current and current deficit, depending on the parameters of the localized states and the transparency of the tunnel barrier.
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Khlus, V.A., Dyomin, A.V. Resonant tunneling in normal metal-superconductor junctions: Low-voltage conductance features and excess current. J Supercond 8, 71–78 (1995). https://doi.org/10.1007/BF00732243
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DOI: https://doi.org/10.1007/BF00732243