超导自旋阀中的自旋转移力矩和磁阻效应
Spin-Transfer Torque and Magnetoresistance in Superconducting Spin-Valves
摘要：
我们研究了铁磁$\mid$超导体$\mid$铁磁自旋阀的自旋转移矩和磁阻，考虑了任意的磁化方向差，并处理了超导体的s波和d波对称性。我们充分考虑了Andreev反射，也自旋三重态的相关性时产生的磁化是非共线的。结果表明，当界面处存在拓扑零能态时，转矩和磁电阻都得到了显著的增强，这与d波超导体相对于界面的晶向为[110]（$d_{xy}$波对称）的情况相同.此外，我们还发现磁电阻随$d_S/ξ$的变化呈现出强烈的振荡和非单调行为，其中$d_S$和$ξ$分别是超导区的层间宽度和超导相干长度.该特征也归因于从尺寸为$d_S\sim 2ξ$的层到尺寸为$d_S\gg 2ξ$的层的交叉，其中对来自零能态的输运的贡献逐渐消失。
英文摘要：
We study the spin-transfer torque and magnetoresistance of a ferromagnet$\mid$superconductor$\mid$ferromagnet spin-valve, allowing for an arbitrary magnetization misorientation and treating both s-wave and d-wave symmetries of the superconductor. We take fully into account Andreev reflection and also the spin-triplet correlations that are generated when the magnetizations are non-collinear. It is found that the torque and magnetoresistance are both strongly enhanced when topological zero-energy states are present at the interfaces, which is the case for d-wave superconductors with a crystallographic orientation of [110] relative to the interface ($d_{xy}$-wave symmetry). Moreover, we find that the magnetoresistance displays a strong oscillatory and non-monotonous behavior as a function of $d_S/ξ$ where $d_S$ and $ξ$ are the interlayer width of the superconducting region and the superconducting coherence length, respectively. This feature is also attributed to the crossover from layers of size $d_S\sim 2ξ$ to layers of size $d_S\gg 2ξ$, where the contribution to transport from zero-energy states gradually vanishes.
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