Thouless energy of a superconductor from non local conductance fluctuations
Centre de Recherches sur les Très Basses Températures (CRTBT), CNRS, BP 166, 38042 Grenoble Cedex 9, France
Corresponding author: a firstname.lastname@example.org
Revised: 4 August 2006
Published online: 13 October 2006
We show that a spin-up electron from a normal metal entering a superconductor propagates as a composite object consisting of a spin-down hole and a pair in the condensate. This leads to a factorization of the non local conductance as two local Andreev reflections at both interfaces and one propagation in the superconductor, which is tested numerically within a one dimensional toy model of reflectionless tunneling. Small area junctions are characterized by non local conductance fluctuations. A treatment ignoring weak localization leads to a Thouless energy inverse proportional to the sample size, as observed in the numerical simulations. We show that weak localization can have a strong effect, and leads to a coupling between evanescent quasiparticles and the condensate by Andreev reflections “internal” to the superconductor.
PACS: 74.50.+r – Tunneling phenomena; point contacts, weak links, Josephson effects / 74.78.Na – Mesoscopic and nanoscale systems / 74.78.Fk – Multilayers, superlattices, heterostructures
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2006