Influence of Andreev reflection on current-voltage characteristics of superconductor/ferromagnet/superconductor metallic weak links

Abstract

We develop a quantitative theory describing the behavior of current-voltage characteristics (CVCs) in superconductor (S)/ferromagnet (F)/superconductor (SFS) weak links with transparent S/F interfaces. The approach of Kümmel, Gunsenheimer, and Nikolsky, developed for S/normal metal (N)/S junctions with an N barrier and based on the solution of time-dependent Bogoliubov-de Gennes equations combined with the time-relaxation model, is generalized to the SFS case. CVCs are calculated as a function of the barrier material parameters: the exchange energy h, the barrier thickness d, and the mean free path l. CVC peculiarities, such as a steep rise in the current and negative differential conductance at a low voltage, as well as the h-dependent position of the peaks, are obtained for a weak exchange energy h lower than or comparable to the superconducting energy gap Δ=Δ(T). They are interpreted to be induced by multiple Andreev reflections, modified in the presence of h in ferromagnets. © 2012 American Physical Society.