Josephson current through a ferromagnetic bilayer: Beyond the quasiclassical approximation
Josephson current through a ferromagnetic bilayer: Beyond the quasiclassical approximation
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通过铁磁双层的约瑟夫森电流：超越准经典近似
DOI：
10.1103/physrevb.100.224514
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发表时间：
2019-12
影响因子：
3.7
通讯作者：
Buzdin A. I
中科院分区：
文献类型：
--
作者：
Meng Hao;Ren Yajie;Villegas Javier E.;Buzdin A. I
基于Bogoliubov-de Gennes方程，给出了复合铁磁双层Josephson结临界电流的精确数值解。我们证明，对于反平行方向的双层磁矩，在双层界面上的势垒的存在导致临界电流的大振荡作为铁磁厚度和/或交换场的函数。因此，值得注意的是，在小的交换场和厚度范围内，磁性导致临界电流的增加。这种效应在低温时很明显，但在接近高温时消失。如果势垒在双层界面处被自旋活性势垒取代，则观察到类似于均匀铁磁约瑟夫森结的常规0-π跃迁。引人注目的是，对于双分子层磁矩的平行方向，自旋活性势垒的存在恢复了反平行情况下的异常行为势垒。这些行为是由库珀对穿过复合势垒的共振隧穿引起的，这种效应与铁磁体交换场存在时依赖自旋的费米矢量有关。
Based on the Bogoliubov–de Gennes equations, we provide an exact numerical solution for the critical current of Josephson junctions with a composite ferromagnetic bilayer. We demonstrate that for the antiparallel orientation of the magnetic moments of the bilayer, the presence of a potential barrier at the bilayer interface results in large oscillations of the critical current as a function of ferromagnet thickness and/or exchange field. Because of this, and remarkably, in the range of small exchange field and thicknesses, the magnetism leads to the increase of the critical current. This effect is well pronounced at low temperature but disappears near Tc. If the potential barrier is replaced by a spin-active barrier at the bilayer interface the conventional 0-π transition, similar to the case of an uniform ferromagnetic Josephson junction, is observed. Strikingly, for a parallel orientation of the magnetic moments of the bilayer, the presence of the spin-active barrier restores the anomalous behavior—potential barrier in the antiparallel case. These behaviors result from the resonant tunneling of Cooper pairs across the composite barrier—an effect related to the spin-dependent Fermi vector in the presence of the ferromagnets’ exchange field.
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