Physics Institute II, University of Cologne , Zülpicher Straße 77 , 50937 Köln , Germany.
Nano Lett. 2018 Aug 8;18(8):5124-5131. doi: 10.1021/acs.nanolett.8b02029. Epub 2018 Jul 25.
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, BiSbTeSe, and Al. The Fermi level can be tuned by gating across the Dirac point, and the high transparency of the Al-BiSbTeSe 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.
一维马约拉纳模式被预测会在基于三维拓扑绝缘体 (TI) 的约瑟夫森结中形成。虽然最近已经报道了在体绝缘 TI 样品上的约瑟夫森结中超流的观测结果，但在这种基于 TI 的约瑟夫森结中观察到的夫琅禾费模式，其有时表现出异常特征，仍未得到很好的理解。在这里，我们报告了我们对由最具体绝缘 TI 材料之一的 BiSbTeSe 和 Al 制成的高度可门控 TI 基约瑟夫森结的研究。费米能级可以通过在狄拉克点处门控来调节，而 Al-BiSbTeSe 界面的高透明度通过高特征电压和多个安德烈夫反射来证明，峰值指数达到 12。在整个门电压范围内观察到具有缺失叶瓣的异常夫琅禾费模式。我们发现，通过采用先进的拟合程序，使用蒙特卡罗算法中的最大熵方法，可以解释异常夫琅禾费模式是由于结中 TI 表面上的非均匀超导电流分布所致。除了建立一种很有前途的制造技术外，这项工作还澄清了关于基于 TI 的约瑟夫森结的一个重要未解决问题。
