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arXiv 1708.05089cond-mat.mes-hallcond-mat.supr-con
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弹道铁磁SQUID中的库珀对分裂

Cooper pair splitting in ballistic ferromagnetic SQUIDs

P. L. Stroganov, Ya. V. Fominov

摘要:

我们考虑半金属铁磁臂内的自旋过滤弹道SQUID。在这种情况下,单线态库珀对不能通过臂,因此约瑟夫森电流完全是由于库珀对分裂,两个电子进入不同的干涉仪臂。为了阐明由于分裂库珀对引起的约瑟夫森输运机制,我们假设臂在短结极限下是单沟道导线。系统的不同几何形状(由臂的长度和在臂之间分裂期间由准粒子获得的相位确定)导致SQUID特性(Andreev能级、电流-相位关系和临界约瑟夫森电流)作为两个控制参数(外部磁通量和两个自旋过滤器的取向差)的函数的定性不同的行为。电流-相位关系可以改变其幅度和形状,特别是,转向π结形式或获得额外的过零点。临界电流可以成为自旋过滤器的取向差和磁通量(在半周期上)的非单调函数。与常规SQUID相比,相对于磁通量的周期性加倍。

英文摘要:

We consider ballistic SQUIDs with spin filtering inside half-metallic ferromagnetic arms. A singlet Cooper pair cannot pass through an arm in this case, so the Josephson current is entirely due to the Cooper pair splitting, with two electrons going to different interferometer arms. In order to elucidate the mechanisms of Josephson transport due to split Cooper pairs, we assume the arms to be single-channel wires in the short-junction limit. Different geometries of the system (determined by the length of the arms and the phases acquired by quasiparticles during splitting between the arms) lead to qualitatively different behavior of the SQUID characteristics (the Andreev levels, the current-phase relation, and the critical Josephson current) as a function of two control parameters, the external magnetic flux and misorientation of the two spin filters. The current-phase relation can change its amplitude and shape, in particular, turning to a pi-junction form or acquiring additional zero crossings. The critical current can become a nonmonotonic function of the misorientation of the spin filters and the magnetic flux (on half of period). Periodicity with respect to the magnetic flux is doubled, in comparison to conventional SQUIDs.

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