Finite-size effects in a nanowire strongly coupled to a thin superconducting shell
Finite-size effects in a nanowire strongly coupled to a thin superconducting shell
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DOI：
10.1103/physrevb.96.125426
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发表时间：
2017-09-19
影响因子：
3.7
通讯作者：
Klinovaja, Jelena
中科院分区：
文献类型：
--
作者：
Reeg, Christopher;Loss, Daniel;Klinovaja, Jelena
研究了一维纳米线与特征尺寸远小于其相干长度的有限超导体强耦合时的邻近效应。这种几何形状已成为越来越相关的，近年来在实验中寻找马约拉纳费米子与薄外延铝壳的发展，形成一个非常强大的接触，无论是铟砷或锑化铟纳米线。然而，到目前为止，还没有理论上的处理在这些系统中的邻近效应已占有限尺寸的超导膜。我们发现，当超导体的能级间距大大超过其能隙时，有限尺寸效应变得非常有害。在没有对超导体的尺寸进行任何微调的情况下（在费米波长的尺度上），隧穿能量尺度必须大于能级间距，以达到在实验中普遍存在的“硬能隙”状态。然而，在这个制度中，大的隧穿能量尺度诱导的纳米线的有效化学势的大的移位，并推动拓扑相变的磁场强度超过Al的临界场。
We study the proximity effect in a one-dimensional nanowire strongly coupled to a finite superconductor with a characteristic size which is much shorter than its coherence length. Such geometries have become increasingly relevant in recent years in the experimental search for Majorana fermions with the development of thin epitaxial Al shells which form a very strong contact with either InAs or InSb nanowires. So far, however, no theoretical treatment of the proximity effect in these systems has accounted for the finite size of the superconducting film. We show that the finite-size effects become very detrimental when the level spacing of the superconductor greatly exceeds its energy gap. Without any fine tuning of the size of the superconductor (on the scale of the Fermi wavelength), the tunneling energy scale must be larger than the level spacing in order to reach the "hard gap" regime which is seen ubiquitously in the experiments. However, in this regime, the large tunneling energy scale induces a large shift in the effective chemical potential of the nanowire and pushes the topological phase transition to magnetic field strengths which exceed the critical field of Al.