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arXiv 0912.0105cond-mat.supr-concond-mat.mes-hall
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超导体-铁磁体点接触谱理论:强自旋极化情况

Theory of superconductor-ferromagnet point contact spectra: the case of strong spin polarization

Roland Grein, Tomas Lofwander, Georgo Metalidis, Matthias Eschrig

摘要:

我们研究了自旋激活散射对超导体(SC)和强自旋极化铁磁体(FM)之间的点接触的Andreev谱的影响,使用最近导出的准经典超导理论的边界条件。我们描述的界面区域的界面散射矩阵的微观模型。我们的模型包括自旋过滤和自旋混合,是非微扰的传输和自旋极化。我们强调的重要性,自旋混合所造成的界面散射,这已被证明是至关重要的创造异国情调的配对相关在这样的结构。我们提供了在不同的情况下,这种影响的可能幅度的估计,并讨论其依赖于各种物理参数。我们的主要发现是界面势的形状对自旋混合效应的大小有着巨大的影响。因此,以前的计算,是基于δ函数或箱形界面势,严重低估了这种影响。因此,我们发现,与现实的界面电位的自旋混合效应可以很容易地大到足以导致自旋极化的子间隙Andreev的SC/sFM点接触的束缚态。此外,我们表明,我们的理论概括了早期模型的基础上的Blonder-Tinkham-Klapwijk方法。

英文摘要:

We study the impact of spin-active scattering on Andreev spectra of point contacts between superconductors(SCs) and strongly spin-polarized ferromagnets(FMs) using recently derived boundary conditions for the Quasiclassical Theory of Superconductivity. We describe the interface region by a microscopic model for the interface scattering matrix. Our model includes both spin-filtering and spin-mixing and is non-perturbative in both transmission and spin polarization. We emphasize the importance of spin-mixing caused by interface scattering, which has been shown to be crucial for the creation of exotic pairing correlations in such structures. We provide estimates for the possible magnitude of this effect in different scenarios and discuss its dependence on various physical parameters. Our main finding is that the shape of the interface potential has a tremendous impact on the magnitude of the spin-mixing effect. Thus, all previous calculations, being based on delta-function or box-shaped interface potentials, underestimate this effect gravely. As a consequence, we find that with realistic interface potentials the spin-mixing effect can easily be large enough to cause spin-polarized sub-gap Andreev bound states in SC/sFM point contacts. In addition, we show that our theory generalizes earlier models based on the Blonder-Tinkham-Klapwijk approach.

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