Evidence for a topological excitonic insulator in InAs/GaSb bilayers

• Published in: Nature communications Vol. 8; no. 1; pp. 1971 - 8
• Main Authors: Du, Lingjie, Li, Xinwei, Lou, Wenkai, Sullivan, Gerard, Chang, Kai, Kono, Junichiro, Du, Rui-Rui
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 07.12.2017; Nature Publishing Group; Nature Portfolio
• Subjects: 639/766/119/2792; 639/766/119/995; CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; Conductance; Critical temperature; Dilution; Electron transport; Excitation; Gallium antimonides; Humanities and Social Sciences; Indium arsenides; Line spectra; Low temperature; MATERIALS SCIENCE; multidisciplinary; Quantum theory; Quantum wells; Resistance; Science; Science (multidisciplinary)
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-017-01988-1

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. Weakly bound electron–hole pairs may condensate in two-dimensional systems, but experimental evidence has been lacking. Here, Du et al. report optical spectroscopic and electronic transport evidences for the formation of an excitonic insulator gap in topological InAs/GaSb quantum wells.