Nanoscale Imaging of Topological Superconductivity in Heterostructures

Harvard University, Cambridge MA

Investigators

Abstract

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.