The goal of this project is to explore the coupling of superconductivity into the conducting surface modes of Topological Insulators (TI) such as Bi2Te3, Bi2Se3, and other related compounds. By making samples with superconducting electrodes separated by the TI, the behavior of superconducting pairs in the spin-orbit correlated surface state can be studied. Such two dimensional systems have been predicted to exhibit p-wave superconductivity and have vortex cores that contain bound Majorana Fermion states, which may form the basis for topologically protected qubits. The samples are fabricated in two coupled molecular beam epitaxy systems, one specializing in the growth of the TI material and the other dedicated to the growth of niobium films. Since the sample remains under ultra-high vacuum conditions during the growth of all layers, the interface is free of contaminants and very transparent junctions between the two materials are obtained. Students working on this project are trained in advanced materials synthesis, nanoscale device fabrication, and low temperature measurement techniques. This provides them with a broad technical background that is useful for work in many areas of materials science and technology.

Nontechnical Abstract

A Topological Insulator (TI) is a new kind of material in which the bulk of a sample is not conducting, but a two dimensional layer on its surface is. Moreover, the conducting surface state is made up of only half of the electrons that a normal conductor has - for an electron with a given momentum, only one spin is present. When superconducting pairs are introduced in such a 2D system with momentum-spin correlations, a new kind of state has been predicted to emerge, a so-called Majorana Fermion (MF). According to theory, this state can be used to construct a long-lived qubit, a quantum bit that can be processed by a quantum circuit that is also topologically protected from decoherence. To study this effect, samples of TIs are made using ultra high vacuum deposition technology. Then superconducting films are deposited on top to introduce superconductivity into the surface modes. Devices are made using nanoscale lithography and advanced etching technology, and they are measured at low temperatures to search for MFs. The students working on this project receive training in a wide range of advanced science and technology preparing them well for developing technologies of the future.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Guebre X. Tessema
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University of Illinois Urbana-Champaign
United States
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