Anomalous Fraunhofer Patterns in Gated Josephson Junctions Based on the Bulk-Insulating Topological Insulator BiSbTeSe2,Nano Letters

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Anomalous Fraunhofer Patterns in Gated Josephson Junctions Based on the Bulk-Insulating Topological Insulator BiSbTeSe2
Nano Letters ( IF 9.6 ) Pub Date : 2018-07-20 00:00:00 , DOI: 10.1021/acs.nanolett.8b02029
Subhamoy Ghatak ₁ , Oliver Breunig ₁ , Fan Yang ₁ , Zhiwei Wang ₁ , Alexey A. Taskin ₁ , Yoichi Ando ₁

Affiliation

One-dimensional Majorana modes are predicated to form in Josephson junctions based on three-dimensional topological insulators (TIs). While observations of supercurrents in Josephson junctions made on bulk-insulating TI samples have been reported recently, the Fraunhofer patters observed in such TI-based Josephson junctions, which sometimes present anomalous features, are still not well-understood. Here, we report our study of highly gate-tunable TI-based Josephson junctions made of one of the most bulk-insulating TI materials, BiSbTeSe₂, and Al. The Fermi level can be tuned by gating across the Dirac point, and the high transparency of the Al–BiSbTeSe₂ interface is evinced by a high characteristic voltage and multiple Andreev reflections, with peak indices reaching 12. Anomalous Fraunhofer patterns with missing lobes were observed in the entire range of gate voltage. We found that, by employing an advanced fitting procedure to use the maximum entropy method in a Monte Carlo algorithm, the anomalous Fraunhofer patterns are explained as a result of inhomogeneous supercurrent distributions on the TI surface in the junction. Besides establishing a highly promising fabrication technology, this work clarifies one of the important open issues regarding TI-based Josephson junctions.

中文翻译：

基于本体绝缘拓扑绝缘子BiSbTeSe _2的门控约瑟夫森结的Fraunhofer异常模式

预测一维Majorana模将在基于三维拓扑绝缘体（TI）的约瑟夫森结中形成。尽管最近已报道了在大量绝缘的TI样品上进行的约瑟夫森结中超电流的观察，但在这种基于TI的约瑟夫森结中有时会出现异常特征的弗劳恩霍夫模式仍然未被很好地理解。在这里，我们报告了对高度门可调的基于TI的约瑟夫逊结的研究，该结是由最绝缘的TI材料之一BiSbTeSe ₂和Al制成的。费米能级可以通过控制狄拉克点上的门以及Al–BiSbTeSe ₂的高透明度来调节较高的特征电压和多次Andreev反射证明了该界面，峰值指数达到12。在整个栅极电压范围内都观察到了具有缺失波瓣的异常Fraunhofer图案。我们发现，通过在蒙特卡洛算法中使用高级拟合程序以使用最大熵方法，可以解释异常的Fraunhofer图案是结中TI表面上不均匀的超电流分布的结果。除了建立一种很有前途的制造技术外，这项工作还阐明了有关基于TI的约瑟夫森结的重要开放问题之一。

更新日期：2018-07-20

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