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arXiv 1405.0918cond-mat.mes-hallcond-mat.supr-con
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电子-电子排斥作用下$s$波超导体与无序正常金属界面的零能束缚态

Zero-energy bound state at the interface between an $s$-wave superconductor and a disordered normal metal with repulsive electron-electron interactions

Christopher R. Reeg, Dmitrii L. Maslov

摘要:

近几年来,由于邻近效应在实现拓扑超导电性中的重要作用,人们对邻近效应又重新产生了兴趣。在这里,我们研究一个超导体-正常金属邻近系统与排斥电子-电子相互作用的正常层。已知的是,在超导体-正常金属界面处没有无序或正常反射的情况下,零能量束缚态形成并局限于界面[Fauchere等人,物理修订版信函82,3336(1999)]。利用准经典超导理论,我们研究了有限无序和界面势垒存在下的态密度的低能行为。我们发现,随着平均自由程的减小,态密度的零能峰变宽和变小。在准弹道极限下,束缚态消除了与非相互作用正常层有关的小间隙,并观察到一个明显的峰。当平均自由程变得与正常层宽相当时,零能峰被强烈抑制,并且小间隙开始发展。在扩散极限下,微间隙被完全恢复,束缚态的所有特征被消除。我们发现,界面势垒不改变的状态密度峰的功能形式,但移动这个峰远离零能量。

英文摘要:

In recent years, there has been a renewed interest in the proximity effect due to its role in the realization of topological superconductivity. Here, we study a superconductor--normal metal proximity system with repulsive electron-electron interactions in the normal layer. It is known that in the absence of disorder or normal reflection at the superconductor--normal metal interface, a zero-energy bound state forms and is localized to the interface [Fauchere et al., Phys. Rev. Lett. 82, 3336 (1999)]. Using the quasiclassical theory of superconductivity, we investigate the low-energy behavior of the density of states in the presence of finite disorder and an interfacial barrier. We find that as the mean free path is decreased, the zero-energy peak in the density of states is broadened and reduced. In the quasiballistic limit, the bound state eliminates the minigap pertinent to a noninteracting normal layer and a distinct peak is observed. When the mean free path becomes comparable to the normal layer width, the zero-energy peak is strongly suppressed and the minigap begins to develop. In the diffusive limit, the minigap is fully restored and all signatures of the bound state are eliminated. We find that an interfacial potential barrier does not change the functional form of the density of states peak but does shift this peak away from zero energy.

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