Conductances in normal and normal/superconductor structures |
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| Affiliation: | 1. School of Aerospace, Mechanical and Manufacturing Engineering, Royal Melbourne Institute of Technology, Melbourne, Australia;2. Energy Flagship, Commonwealth Scientific and Industrial Research Organisation, Newcastle, Australia;1. School of Materials Engineering, Purdue University, West Lafayette, IN 47907, United States;2. School of Applied Sciences and Engineering Technology, Ivy Tech Community College, Lafayette, IN 47905, United States;1. Donostia International Physics Center, 20018 Donostia-San Sebastian, Spain;2. Department of Condensed Matter Physics, University of the Basque Country UPV/EHU, Apartado 644, 48080 Bilbao, Spain;3. Department of Physics and Institute of Condensed Matter Theory, University of Illinois at Urbana-Champaign, IL 61801, USA;4. Energy Technologies Area, Lawrence Berkeley National Laboratory, Berkeley, USA;5. Materials Science and Engineering, University of California, Berkeley, USA;6. Department of Physics, University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland;7. IKERBASQUE, Basque Foundation for Science, Maria Diaz de Haro 3, 48013 Bilbao, Spain |
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| Abstract: | We study theoretically electronic transport through a normal-metal/superconductor (NS) interface and show that more than one conductance may be defined, depending on the pair of chemical potentials whose difference one chooses to relate linearly to the current. We argue that the situation is analogous to that found for purely normal transport, where different conductance formulae can be invoked. We revisit the problem of the ‘right’ conductance formula in a simple language, and analyze its extension to the case of mesoscopic superconductivity. The well-known result that the standard conductance of an NS interface becomes 2 (in units of 2 e2 / h) in the transmissive limit is viewed here in a different light. We show that it is not directly related to the presence of Andreev reflection, but rather to a particular choice of chemical potentials. This value of 2 is measurable because only one single-contact resistance is involved in a typical experimental setup, in contrast with the purely normal case where two of them intervene. We introduce an alternative NS conductance that diverges in the transmissive limit due to the inability of Andreev reflection to generate a voltage drop. We illustrate numerically how different choices of chemical potential can yield widely differingI –V curves for a given NS interface. |
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