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Finite-size effects in a nanowire strongly coupled to a thin superconducting shell
Physical Review B ( IF 3.7 ) Pub Date : 2017-09-19 00:00:00 , DOI: 10.1103/physrevb.96.125426
Christopher Reeg , Daniel Loss , Jelena Klinovaja

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.

中文翻译:

强耦合到薄超导壳的纳米线中的有限尺寸效应

我们研究了一维纳米线中与有限超导体强耦合的邻近效应,该超导体的特征尺寸比其相干长度短得多。近年来,随着薄外延铝壳的发展,这种几何形状在马约拉纳费米子的实验研究中变得越来越重要,铝壳形成了与InAs或InSb纳米线的非常牢固的接触。然而,到目前为止,在这些系统中对邻近效应的理论处理还没有说明超导膜的有限尺寸。我们表明,当超导体的能级间距大大超过其能隙时,有限尺寸效应将变得非常有害。在不对超导体的尺寸进行任何微调的情况下(以费米波长为尺度),为了达到“硬间隙”状态,隧穿能级必须大于能级间距,这在实验中很普遍。然而,在这种情况下,较大的隧穿能级引起纳米线的有效化学势的大偏移,并将拓扑相变推向磁场强度,该磁场强度超过了Al的临界场。
更新日期:2017-09-19
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