Nanoscale Imaging of Topological Superconductivity in Heterostructures

摘要：除了众所周知的负电荷外，电子还具有另一种性质，称为“自旋”，类似于旋转轴，可以指向任何方向。理想的拓扑绝缘体（TI）是一种内部是电绝缘的材料，但其表面是一种特殊的金属，在这种金属中，电子自旋被防止反向散射，从而消除了当今微电子中不必要的加热的主要来源。这些表面特性使其成为两种革命性未来技术的有希望的候选者：“自旋电子学”，一种非常低功耗的传统电子产品替代品，以及“量子计算”，一种全新的快速解决计算密集型问题的方法。然而，在过去5年里发现的第一代拓扑材料，其内部存在不必要的电子“泄漏”，这破坏了它们有希望的表面性能。该奖项支持两组平行实验，旨在发现完美的拓扑绝缘体，并设计拓扑和其他材料之间的界面，这些材料有望实现量子计算应用。该实验结合了两种先进的原子尺度材料合成和表征技术：分子束外延和扫描隧道显微镜。对拓扑绝缘体在自旋电子学和量子计算方面的理解和应用将从这个项目中得到根本性的进步。该奖项还支持一名博士后和一名研究生的教育和培训。技术摘要：理想拓扑绝缘体（TI）是一种具有绝缘体，但具有拓扑保护的导电表面状态的材料，在这种状态下，自旋极化电子被阻止反向散射。这些特性使它成为实现两种变革性未来技术的有希望的候选者：“自旋电子学”，它可以绕过目前限制传统电子学的严重功耗问题，以及“拓扑量子计算”，它为当今最好的量子比特的短退相干时间提供了一种选择。然而，被广泛研究的第一代Bi2X3拓扑“绝缘体”由于显然不可避免的自掺杂而遭受不必要的体传导。该奖项支持两种平行的实验方法来规避这些挑战。一种是利用扫描隧道显微镜（STM）在真正的块状绝缘体上搜索拓扑表面态，例如拓扑近藤绝缘体。并行方法是在密度泛函理论计算的指导下，利用结合分子束外延和STM系统来设计拓扑半金属锑超导体异质结构。这种方法的意义在于首次实现和研究拓扑p波超导性，这将对非常规超导体领域产生更广泛的影响，并为最终寻找拓扑量子计算应用核心的马约拉纳费米子提供一个平台。该奖项还支持一名博士后和一名研究生在先进材料合成和表征技术方面的教育和培训。

Non technical Abstract: In addition to their well-known negative electric charge, electrons carry a second property called "spin", akin to an axis of rotation which may point in any direction. An ideal topological insulator (TI) is a material whose interior is electrically insulating, but whose surface is a special metal where electron spins are prevented from backscattering, removing the primary source of unwanted heating in today's microelectronics. These surface properties make TIs promising candidates to enable two transformative future technologies: "spintronics," a very low power replacement for conventional electronics, and "quantum computing," a completely new method for rapidly solving computationally intensive problems. However, the first generation of topological materials, discovered over the last 5 years, has suffered from unwanted "leakage" of electrons through their interiors, which undermines their promising surface properties. This award supports two parallel sets of experiments aimed at discovering perfect topological insulators and at engineering the interfaces between topological and other materials which are predicted to enable quantum computing applications. The experiments combine two advanced atomic-scale material synthesis and characterization techniques: molecular beam epitaxy and scanning tunneling microscopy. A fundamental advancement of the understanding and utility of topological insulators towards spintronics and quantum computing would be expected from this project. This award also supports the education and training of one postdoctoral fellow and one graduate student. Technical Abstract:An ideal topological insulator (TI) is a material with an insulating bulk, but a topologically protected conducting surface state on which spin-polarized electrons are prevented from backscattering. These properties make TIs promising candidates to enable two transformative future technologies: "spintronics," which may circumvent the severe power dissipation problems now limiting conventional electronics, and "topological quantum computing," which provides an alternative to the short decoherence times in the best present-day qubits. However, the highly-studied first-generation Bi2X3 topological "insulators" suffer from unwanted bulk conduction due to apparently unavoidable self-doping. This award supports two parallel experimental approaches to circumvent these challenges. One is to use scanning tunneling microscopy (STM) to search for topological surface states on true bulk insulators, such as topological Kondo insulators. The parallel approach is to engineer topological semimetal antimony-superconductor heterostructures using a combined molecular beam epitaxy and STM system, with guidance from density functional theory calculations. The significance of this approach lies in the first achievement and study of topological p-wave superconductivity, which would have high impact on the field of unconventional superconductors more broadly and also provide a playground for the eventual search for the Majorana fermion at the heart of topological quantum computing applications. The award also supports the education and training of one postdoctoral fellow and one graduate student in advanced material synthesis and characterization techniques.