Theory of proximity effect in superconductor/ferromagnet heterostructuresстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 29 мая 2015 г.
Аннотация:We present a microscopic theory of the proximity effect in the ferromagnet/superconductor/ferromagnet (F/S/F) nanostructures where S is an s-wave low-T(c) superconductor and F's are layers of 3d transition ferromagnetic metal. Our approach is based on the direct analytical solution of Gor'kov equations for the normal and anomalous Green's functions together with a self-consistent evaluation of the superconducting order parameter. We take into account the elastic spin-conserving scattering of the electrons assuming s-wave scattering in the S layer and s-d scattering in the F layers. In accordance with previous quasiclassical theories, we found that due to exchange field in the ferromagnet the anomalous Green's function F(z) exhibits the damping oscillations in the F layer as a function of distance z from the S/F interface. In the given model, a half of the period of oscillations is determined by the length xi(m)(0)=piv(F)/epsilon(ex), where v(F) is the Fermi velocity and epsilon(ex) is the exchange field, while damping is governed by the length l(0)=(1/l(up arrow)+1/l(down arrow))(-1), with l(up arrow) and l(down arrow) being spin-dependent mean free paths in the ferromagnet. The superconducting transition temperature T(c)(d(F)) of the F/S/F trilayer shows the damping oscillations as a function of the F-layer thickness d(F) with period xi(F)=pi/rootmepsilon(ex), where m is the effective electron mass. The oscillations of T(c)(d(F)) are a consequence of the oscillatory behavior of the superconducting order parameter at the S/F interface vs thickness d(F), which in turn is caused by the oscillations of F(z) in the F region. We show that strong spin-conserving scattering either in the superconductor or in the ferromagnet significantly suppresses these oscillations. The calculated T(c)(d(F)) dependences are compared with existing experimental data for Fe/Nb/Fe trilayers and Nb/Co multilayers.