DMREF: Collaborative Research: Discovering Insulating Topological Insulators

University Of California-Davis, Davis CA

Investigators

Abstract

Non-technical abstract: At the heart of electronic devices lies silicon, a semiconductor material that can be made pure enough for high performance and is amenable to mass production. While such circuitry is continually improving, silicon is unable to exhibit quantum phenomena required for complete solutions in weather prediction, genomics, and secure encryption. A new class of materials, the so-called topological insulators, holds the promise to realize such phenomena and revolutionize computing. Topological insulators are, in theory, non-metallic in the interior of the material but behave like a metal at the surface. In addition, the quantum character of these metallic electrons can be switched, which is the basic information processing function. While known topological insulators demonstrate the metallic surface state, these materials have not been made pure enough for incorporating into electronic devices. Specifically, they are not yet insulating in the interior. This project will seek to find new topological insulators and to engineer them to levels of purity needed for an insulating interior and satisfy the performance demands of electronic circuits. The project will impact the electronics industry as well as train graduates skilled in the computational and experimental techniques of this new class of materials. Technical abstract: The goal of the project is to create topological insulator materials that are pure enough in the bulk to exhibit true insulating behavior. Topological insulators are found among high-Z atom containing semiconductors with band gaps small enough that the spin-orbit coupling related to the large Z-number can invert the conduction and valence band. These materials must also possess spatial inversion symmetry for the relevant orbitals. The project will explore candidate materials classes among pseudo-binary and pyrochlore-related structures containing heavy metals such as Ir, Re, and Os. Materials synthesis by solid state chemistry techniques will be guided by simulations based on density functional theory. Promising candidate materials will be synthesized in single crystal form by appropriate methods including vapor transport, zone refinement, and growth from flux. Crystalline specimens will be studied with angle resolved photoemission spectroscopy and conventional charge transport techniques. Prototype transistor devices will be fabricated on a smaller subset of these systems. The results at each measurement stage will be fed back to the theory and synthesis efforts.