Evidence for a topological excitonic insulator in InAs/GaSb bilayers

Lingjie Du, Xinwei Li, Wenkai Lou, Gerard Sullivan, Kai Chang (), Junichiro Kono () and Rui-Rui Du ()
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Lingjie Du: Rice University
Xinwei Li: Rice University
Wenkai Lou: Institute of Semiconductors, Chinese Academy of Sciences
Gerard Sullivan: Teledyne Scientific and Imaging
Kai Chang: Institute of Semiconductors, Chinese Academy of Sciences
Junichiro Kono: Rice University
Rui-Rui Du: Rice University

Nature Communications, 2017, vol. 8, issue 1, 1-8

Abstract: Abstract Electron–hole pairing can occur in a dilute semimetal, transforming the system into an excitonic insulator state in which a gap spontaneously appears at the Fermi surface, analogous to a Bardeen–Cooper–Schrieffer (BCS) superconductor. Here, we report optical spectroscopic and electronic transport evidence for the formation of an excitonic insulator gap in an inverted InAs/GaSb quantum-well system at low temperatures and low electron–hole densities. Terahertz transmission spectra exhibit two absorption lines that are quantitatively consistent with predictions from the pair-breaking excitation dispersion calculated based on the BCS gap equation. Low-temperature electronic transport measurements reveal a gap of ~2 meV (or ~25 K) with a critical temperature of ~10 K in the bulk, together with quantized edge conductance, suggesting the occurrence of a topological excitonic insulator phase.

Date: 2017
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DOI: 10.1038/s41467-017-01988-1

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