Observation of room temperature excitons in an atomically thin topological insulator

Marcin Syperek, Raul Stühler, Armando Consiglio, Paweł Holewa, Paweł Wyborski, Łukasz Dusanowski, Felix Reis, Sven Höfling, Ronny Thomale, Werner Hanke, Ralph Claessen (), Domenico Sante () and Christian Schneider ()
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Marcin Syperek: Wrocław University of Science and Technology
Raul Stühler: Universität Würzburg
Armando Consiglio: Universität Würzburg
Paweł Holewa: Wrocław University of Science and Technology
Paweł Wyborski: Wrocław University of Science and Technology
Łukasz Dusanowski: Wrocław University of Science and Technology
Felix Reis: Universität Würzburg
Sven Höfling: Universität Würzburg
Ronny Thomale: Universität Würzburg
Werner Hanke: Universität Würzburg
Ralph Claessen: Universität Würzburg
Domenico Sante: University of Bologna
Christian Schneider: University of Oldenburg

Nature Communications, 2022, vol. 13, issue 1, 1-7

Abstract: Abstract Optical spectroscopy of ultimately thin materials has significantly enhanced our understanding of collective excitations in low-dimensional semiconductors. This is particularly reflected by the rich physics of excitons in atomically thin crystals which uniquely arises from the interplay of strong Coulomb correlation, spin-orbit coupling (SOC), and lattice geometry. Here we extend the field by reporting the observation of room temperature excitons in a material of non-trivial global topology. We study the fundamental optical excitation spectrum of a single layer of bismuth atoms epitaxially grown on a SiC substrate (hereafter bismuthene or Bi/SiC) which has been established as a large-gap, two-dimensional (2D) quantum spin Hall (QSH) insulator. Strongly developed optical resonances are observed to emerge around the direct gap at the K and K’ points of the Brillouin zone, indicating the formation of bound excitons with considerable oscillator strength. These experimental findings are corroborated, concerning both the character of the excitonic resonances as well as their energy scale, by ab-initio GW and Bethe-Salpeter equation calculations, confirming strong Coulomb interaction effects in these optical excitations. Our observations provide evidence of excitons in a 2D QSH insulator at room temperature, with excitonic and topological physics deriving from the very same electronic structure.

Date: 2022
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DOI: 10.1038/s41467-022-33822-8

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