自旋混合库珀对引起的Josephson电流

Josephson current induced by spin-mixing Cooper pairs

通过求解Bogoliubov-de Gennes方程研究一维S/FL-F-FR/S结中Josephson电流的输运特性,其中S和F分别是超导体和铁磁体,FL,R是左右两侧具有非共线磁矩的界面层.研究发现,FL和FR界面能够产生自旋混合和自旋翻转效应,该效应能够将S内一部分自旋单重对转化为F内自旋相同的三重对.对于短S/FL-F-FR/S结,F层内同时存在自旋单重对和自旋相同的三重对.于是,随着铁磁交换场和界面磁矩偏转角度差的增加,临界电流在一个基准面上振荡.若F转变为半金属,则F内仅剩自旋相同的三重对,临界电流的振荡特征消失.此外,FL和FR界面还能起到普通势垒的作用.这将导致临界电流随着铁磁厚度的增加展现出双重振荡行为,其中长波振荡源于铁磁体内自旋单重对的位相变化,短波振荡是由自旋单重对和自旋相同的三重对经过两个界面势垒时的共振隧穿效应引起的.

Based on the Bogoliubov-de Gennes equations,we investigate the transport of the Josephson current in a one-dimensional S/FL-F-FR/S junction,where S and F are superconductor and ferromagnet,and FL,R are the left and right interfaces with noncollinear magnetizations.It is found that the FL and FR interfaces can induce spin-mixing and spin-flip effects,which can transform a part of spin-singlet pairs in the S into equal-spin triplet pairs in the F.For the short S/FL-F-FR/S junction,the spin-singlet pairs and the equal-spin triplet pairs can survive in the F layer.Therefore,with the increase of the ferromagnetic exchange field and the angle difference of interface magnetization rotation,the critical current oscillates on a base level.If the F is transformed into half-metal,only the equal-spin triple pairs exist in the F layer,and the oscillation characteristic of critical current disappears.In addition,the FL and FR interfaces can work as conventional potential barriers.As a result,the critical current exhibits double oscillation behaviors with the increase of ferromagnetic thickness,in which the long-wave oscillation arises from the phase change of the spin-singlet pairs in the ferromagnetic layer,and the short-wave oscillation is caused by the resonant tunneling effect when the spin-singlet pairs and the equal-spin triplet pairs pass through two interfacial barriers.