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Sean Hart, Department of Physics, Harvard University, Cambridge, MA, will present seminar. Professor Katja Nowack, host.

Seminar Title: Induced Superconductivity and Unconventional Pairing in HgTe/HgCdTe Quantum Wells

Abstract: Topological insulators are a newly discovered phase of matter characterized by a gapped bulk surrounded by novel conducting boundary states. Since their theoretical discovery, these materials have encouraged intense efforts to study their properties and capabilities. Among the most striking results of this activity are proposals to engineer a new variety of superconductor at the surfaces of topological insulators. These topological superconductors would be capable of supporting localized Majorana fermions, particles whose braiding properties have been proposed as the basis of a fault-tolerant quantum computer. Despite the clear theoretical motivation, a conclusive realization of topological superconductivity remains an outstanding experimental goal. Here we present measurements of superconductivity induced in two-dimensional HgTe/HgCdTe quantum wells, a material which becomes a quantum spin Hall insulator when the well width exceeds dC = 6.3 nm. In wells that are 7.5 nm wide, we find that supercurrents are confined to the one-dimensional sample edges as the bulk density is depleted.  Our Josephson interferometry measurements confirm the topological nature of the system and provide a measurement of the edge channel widths.   Furthermore, when the chemical potential is tuned into the conduction band, application of an in-plane magnetic field results in unconventional superconductivity with triplet pairing.

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