Tailoring the Fulde‐Ferrell‐Larkin‐Ovchinnikov state

Abstract

–to80mmtimes7mm,andcor-respondingly its thickness to 10 nm,and you have an idea about the pre-cision and control necessary to cre-ate thinfilmsin experimentslike theone published recently in Annalender Physik by Jan-Michael Kehrleand co-workers [1]. The motivationforcreatingsuchextraordinarilythinfilms over comparatively large areaswas a prediction that if a thin layerof a conventional superconductor issandwiched between two ferromag-netic films, then the superconduct-ing transition temperature of thistrilayer structure, after initially be-ing suppressed, would show a re-entrance behaviour when the thick-ness of one or both of the ferromag-neticlayers isvaried.The mechanism for such a re-entrant behaviour of the supercon-ducting critical temperature can ul-timately be traced back to the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)effect. Peter Fulde and Richard Fer-rell, working at the time at the Uni-versity of Maryland, published theirarticle in August 1964 in Physical Re-view B (Ref. 3 in [1]). Independently,working at the Moscow Physico-Technical Institute, Anatoly Larkinand Yuri Ovchinnikov published inSeptember1964anarticleaboutsim-ilar effects in Zhurnal Eksperimen-tal’noi i Teoricheskoi Fiziki (whichappeared translated in March 1965in SovietPhysics JETP) (Ref.4 in[1]).Figure (online color at: www.ann-phys.org) IllustrationoftheFulde-Ferrell-Larkin-Ovchinnikov effect, leading tospatial oscillations as well as to singlet-tripletmixingofthesuperconductingpairamplitudesinaferromagnet.The main physical mechanismof the FFLO effect is described inFig. 1 (modified after [2]). Considersuperconductivity in a weakly spin-polarised ferromagnetic material.Electronic spin bands are shiftedwith respect to each other by anamount 2