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arXiv 2007.02793cond-mat.mes-hall
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超导拓扑绝缘体边缘磁链中的增强Majorana束缚态

Enhanced Majorana bound states in magnetic chains on superconducting topological insulator edges

Raphael L. R. C. Teixeira, Dushko Kuzmanovski, Annica M. Black-Schaffer, Luis G. G. V. Dias da Silva

摘要:

在凝聚态系统中形成马约拉纳束缚态(MBSs)的最有希望的机制涉及接近超导材料的一维系统(例如半导体纳米线、磁链和量子自旋霍尔绝缘体(QSHI)边缘)。这些选项中的每一个之间的选择涉及若干因素之间的权衡,例如结果的再现性、系统可调谐性和所得MBS的鲁棒性。在这篇文章中,我们提出,这两个系统的组合,即一个磁链沉积在QSHI边缘接触超导表面,提供了一个更好的选择的可调谐性和MBS的鲁棒性相比,磁链沉积在散装。我们研究了QSHI边缘如何与磁链相互作用,以及边缘邻近如何影响拓扑相位。我们发现,MBSs的边缘附近可以实现较低的化学势和塞曼场比内部的散装,独立的链的磁顺序(铁磁或螺旋顺序)。链中不同的磁序改变了整个相图,甚至抑制了位于QSHI边缘的链中发现的无边界拓扑相。此外,我们通过计算不同配置的马约拉纳极化(MP)来量化MBS的“质量”。对于位于边缘的链,MP已经接近其最大值(对于短链)。对于位于远离边缘的链条,需要更长的链条以获得与位于边缘的链条相同的质量。MP还与间隙内状态同相振荡,这是相对出乎意料的,因为能谱中的峰对应于MBS的较强重叠。

英文摘要:

The most promising mechanisms for the formation of Majorana bound states (MBSs) in condensed matter systems involve one-dimensional systems (such as semiconductor nanowires, magnetic chains, and quantum spin Hall insulator (QSHI) edges) proximitized to superconducting materials. The choice between each of these options involves trade-offs between several factors such as reproducibility of results, system tunability, and robustness of the resulting MBS. In this article, we propose that a combination of two of these systems, namely a magnetic chain deposited on a QSHI edge in contact with a superconducting surface, offers a better choice of tunability and MBS robustness compared to magnetic chain deposited on bulk. We study how the QSHI edge interacts with the magnetic chain, and see how the topological phase is affected by edge proximity. We show that MBSs near the edge can be realized with lower chemical potential and Zeeman field than the ones inside the bulk, independently of the chain's magnetic order (ferromagnetic or spiral order). Different magnetic orderings in the chain modify the overall phase diagram, even suppressing the boundless topological phase found in the bulk for chains located at the QSHI edge. Moreover, we quantify the "quality" of MBSs by calculating the Majorana Polarization (MP) for different configurations. For chains located at the edge, the MP is close to its maximum value already for short chains. For chains located away from the edge, longer chains are needed to attain the same quality as chains located at the edge. The MP also oscillates in phase with the in-gap states, which is relatively unexpected as peaks in the energy spectrum corresponds to stronger overlap of MBSs.

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