DMREF: Collaborative Research: Discovering Insulating Topological Insulators

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Non-technical abstract:At the heart of electronic devices lies silicon, a semiconductor material that can be madepure enough for high performance and is amenable to mass production. While suchcircuitry is continually improving, silicon is unable to exhibit quantum phenomenarequired for complete solutions in weather prediction, genomics, and secure encryption.A new class of materials, the so-called topological insulators, holds the promise torealize such phenomena and revolutionize computing. Topological insulators are, intheory, 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 isthe basic information processing function. While known topological insulatorsdemonstrate the metallic surface state, these materials have not been made pure enoughfor incorporating into electronic devices. Specifically, they are not yet insulating in theinterior. This project will seek to find new topological insulators and to engineer them tolevels of purity needed for an insulating interior and satisfy the performance demands ofelectronic circuits. The project will impact the electronics industry as well as traingraduates skilled in the computational and experimental techniques of this new class ofmaterials.Technical abstract:The goal of the project is to create topological insulator materials that are pure enough inthe bulk to exhibit true insulating behavior. Topological insulators are found amonghigh-Z atom containing semiconductors with band gaps small enough that the spin-orbitcoupling 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 andpyrochlore-related structures containing heavy metals such as Ir, Re, and Os. Materialssynthesis by solid state chemistry techniques will be guided by simulations based ondensity functional theory. Promising candidate materials will be synthesized in singlecrystal form by appropriate methods including vapor transport, zone refinement, andgrowth from flux. Crystalline specimens will be studied with angle resolvedphotoemission spectroscopy and conventional charge transport techniques. Prototypetransistor devices will be fabricated on a smaller subset of these systems. The results ateach measurement stage will be fed back to the theory and synthesis efforts.