具有内禀Rashba-Dresselhaus自旋轨道耦合的超导-铁磁体混合体的临界温度和超导谱
Critical Temperature and Tunneling Spectroscopy of Superconductor-Ferromagnet Hybrids with Intrinsic Rashba-Dresselhaus Spin-Orbit Coupling
摘要：
从理论上研究了具有内禀自旋轨道耦合的超导/铁磁体混合结构中邻近效应在态密度和临界温度上的表现。为了描述一个一般的情况下，我们允许Rashba和Dresselhaus类型的自旋轨道耦合。我们的结果是通过准经典超导理论，扩展到包括Usadel方程和Kupriyanov-Lukichev边界条件的自旋轨道耦合。与以前的工作不同，我们推导出了具有自旋轨道耦合的Usadel方程的Riccati参数化，这使我们能够解决完全邻近机制。首先，我们考虑SF双层和SFS三层中的态密度，在后一种情况下的光谱特征对两个超导体之间的相位差敏感。我们发现，自旋轨道耦合的存在下，由于其在创建自旋三重态库珀对的作用，在态密度留下清晰的光谱指纹。与没有自旋-轨道耦合的SF和SFS结构不同，在这种情况下，态密度强烈地依赖于磁化方向。我们发现，即使在强交换场$h \gg Δ$存在下，自旋轨道耦合也能稳定单重态超导。这导致了磁可调微型间隙的可能性：改变交换场的方向打开和关闭微型间隙。我们还确定了如何的临界温度$T_c$的SF双层的自旋轨道耦合的影响，并证明了一个可以实现一个自旋阀效应与一个单一的铁磁体。我们发现$T_c$表现出高度的非单调行为，作为磁化方向和自旋轨道耦合的类型和方向的函数，提供了一种新的方法来施加控制邻近结构的超导电性。
英文摘要：
We investigate theoretically how the proximity effect in superconductor/ferromagnet hybrid structures with intrinsic spin-orbit coupling manifests in the density of states and critical temperature. To describe a general scenario, we allow for both Rashba and Dresselhaus type spin-orbit coupling. Our results are obtained via the quasiclassical theory of superconductivity, extended to include spin-orbit coupling in the Usadel equation and Kupriyanov--Lukichev boundary conditions. Unlike previous works, we have derived a Riccati parametrization of the Usadel equation with spin-orbit coupling which allows us to address the full proximity regime. First, we consider the density of states in both SF bilayers and SFS trilayers, where the spectroscopic features in the latter case are sensitive to the phase difference between the two superconductors. We find that the presence of spin-orbit coupling leaves clear spectroscopic fingerprints in the density of states due to its role in creating spin-triplet Cooper pairs. Unlike SF and SFS structures without spin-orbit coupling, the density of states in the present case depends strongly on the direction of magnetization. We show that the spin-orbit coupling can stabilize singlet superconductivity even in the presence of a strong exchange field $h \gg Δ$. This leads to the possibility of a magnetically tunable minigap: changing the direction of the exchange field opens and closes the minigap. We also determine how the critical temperature $T_c$ of an SF bilayer is affected by spin-orbit coupling and demonstrate that one can achieve a spin-valve effect with a single ferromagnet. We find that $T_c$ displays highly non-monotonic behavior both as a function of the magnetization direction and the type and direction of the spin-orbit coupling, offering a new way to exert control over the superconductivity of proximity structures.
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