Charge transport through spin-polarized tunnel junction between two spin-split superconductors
Mikel Rouco, Subrata Chakraborty, Faluke Aikebaier, V. N. Golovach, Elia Strambini, Jagadeesh S. Moodera, Francesco Giazotto, Tero T. Heikkilä, F. Sebastian Bergeret
研究了自旋极化隧穿势垒连接的两个自旋分裂超导体之间的结的输运性质。超导体（S）中的自旋分裂场是由相邻的具有任意磁化强度的铁磁绝缘层（FI）引起的。本研究的目的是双重的：一方面，我们提出了一个基于准经典格林函数的理论框架来计算通过结的约瑟夫森和准粒子电流，我们的理论预测了隧道微分电导$dI/dV$的定性新结果，当两个超导体的自旋分裂场是非共线的。我们还讨论了如何基于FI/S结可以用来实现具有恒定的几何相移的电流相位关系的反常约瑟夫森结。因此，它们可以在S电极之间没有相位差的情况下表现出自发的三重态超电流。另一方面，我们显示的EuS/Al/Al $_2$ O $_3$ /EuS/Al结的平面隧道光谱的结果，并使用我们的理论模型再现所获得的$dI/dV$曲线。理论和实验之间的比较揭示了有关的结的本征参数，如超导序参量的大小，自旋分裂字段和自旋弛豫，以及有关的两个EuS膜的属性，作为它们的形态，畴结构和磁各向异性的信息。
英文摘要：
We investigate transport properties of junctions between two spin-split superconductors linked by a spin-polarized tunneling barrier. The spin-splitting fields in the superconductors (S) are induced by adjacent ferromagnetic insulating (FI) layers with arbitrary magnetization. The aim of this study is twofold: On the one hand, we present a theoretical framework based on the quasiclassical Green's functions to calculate the Josephson and quasiparticle current through the junctions in terms of the different parameters characterizing it. Our theory predicts qualitative new results for the tunneling differential conductance, $dI/dV$, when the spin-splitting fields of the two superconductors are non-collinear. We also discuss how junctions based on FI/S can be used to realize anomalous Josephson junctions with a constant geometric phase shift in the current-phase relation. As a result, they may exhibit spontaneous triplet supercurrents in the absence of a phase difference between the S electrodes. On the other hand, we show results of planar tunneling spectroscopy of a EuS/Al/Al$_2$O$_3$/EuS/Al junction and use our theoretical model to reproduce the obtained $dI/dV$ curves. Comparison between theory and experiment reveals information about the intrinsic parameters of the junction, such as the size of the superconducting order parameter, spin-splitting fields and spin relaxation, and also about properties of the two EuS films, as their morphology, domain structure, and magnetic anisotropy.
Enhanced Macroscopic Quantum Tunneling in Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ Intrinsic Josephson Junction Stacks
我们用微波辐射研究了Bi $_2$ Sr $_2$ CaCu $_2$ O $_{8+δ}$本征约瑟夫森结在毫开尔文温度下的宏观量子隧穿.测量结果表明，均匀切换N结堆的逃逸率是约$N^2$倍高于具有相同的等离子体频率的单个结。我们认为，这种巨大的增强堆栈中的宏观量子隧穿率是由电流的波动，发生在由环境的阻抗加载的结的串联阵列。
