Berlin 2012 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 33: Superconductivity, Measuring Devices, Matter at Low Temperature: Poster Session

TT 33.61: Poster

Wednesday, March 28, 2012, 15:00–19:00, Poster B

Multiply gapped density of states in a normal metal in contact with a superconductor — •Johannes Reutlinger¹, Yuli V. Nazarov², Leonid I. Glazman³, and Wolfgang Belzig¹ — ¹Department of Physics, University of Konstanz, 78457 Konstanz, Germany — ²Kavli Institute of Nanoscience Delft, Delft University of Technology, 2628 CJ Delft, Netherlands — ³Department of Physics, Yale University, New Haven CT 06511-8499, USA

The spectral properties of a normal metal adjacent to a superconductor are strongly dependent on the characteristic mesoscopic energy scale - the Thouless energy E_Th - and the strength of the connection. In this work, we predict that the local density of states (LDOS), besides the well know minigap ∼ E_Th, can exhibit a multiple gap structure, which strongly depends on the type of the contact. For ballistic contacts we calculate these secondary gaps analytically in the framework of quantum circuit theory of mesoscopic transport. The secondary gaps are absent in the case of tunnel contacts. In the general case the equations are solved numerically for more realistic contacts, like for example diffusive connectors or dirty interfaces, which are characterized by continuous distributions of transmission eigenvalues between 0 and 1. We find that the gap vanishes in these cases, but the density of states is still suppressed around the superconducting gap edge. Distribution functions with a stronger weight at higher transmissions can be modeled through asymmetric ballistic double junctions, which even exhibit multiple gaps. Such spectral signatures are fundamental to disordered nanoscopic conductors and experimentally accessible.