Magnetoresistive oscillations in a doubly connected SFS interferometer with a ferromagnetic segment longer than the thermal coherence length

Abstract

The conductance of ferromagnetic Ni samples of macroscopic length between F/S interfaces closed by a superconductor indium (an SNS system in the Andreev interferometer geometry) is investigated. The macroscopic size of the system makes it possible to measure directly the conductance of each of the elements of the branched AI circuit and to arrange conditions under which the contribution of side effects, reminiscent of the proximity effect, are minimal. The hc/2e oscillations of the resistance with respect to magnetic field (the Aharonov — Bohm effect in disordered conductors), with an amplitude corresponding to the positive interference contribution to the resistance of an F/S interfacial region with a thickness of the order of the coherence length of the subgap excitations upon Andreev reflection in the presence of an exchange field typical for ferromagnetic materials (∼ 1 nm), are observed for the first time at lengths of the ferromagnetic segments exceeding the typical mesoscopic scale (∼ lμm) by more than a factor of 103.