Evidence for equilibrium exciton condensation in monolayer WTe2
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- University of Washington, Seattle, WA (United States); OSTI
- University of Washington, Seattle, WA (United States)
- University of California, Riverside, CA (United States)
- Consiglo Nazionale delle Richerche (CNR)-NANO, Modema (Italy); Shahid Beheshti University, Tehran (Italy)
- Consiglo Nazionale delle Richerche (CNR)-NANO, Modema (Italy)
- Tor Vergata University of Rome (Italy)
- Consiglo Nazionale delle Richerche (CNR)-NANO, Modema (Italy); University of Modena and Reggio Emilia, Modena (Italy)
We present evidence that the two-dimensional bulk of monolayer WTe2 contains electrons and holes bound by Coulomb attraction—excitons—that spontaneously form in thermal equilibrium. On cooling from room temperature to 100 K, the conductivity develops a V-shaped dependence on electrostatic doping, while the chemical potential develops a step at the neutral point. These features are much sharper than is possible in an independent-electron picture, but they can be accounted for if electrons and holes interact strongly and are paired in equilibrium. Our calculations from first principles show that the exciton binding energy is larger than 100 meV and the radius as small as 4 nm, explaining their formation at high temperature and doping levels. Below 100 K, more strongly insulating behaviour is seen, suggesting that a charge-ordered state forms. The observed absence of charge density waves in this state is surprising within an excitonic insulator picture, but we show that it can be explained by the symmetries of the exciton wavefunction. Therefore, in addition to being a topological insulator, monolayer WTe2 exhibits strong correlations over a wide temperature range.
- Research Organization:
- Columbia University, New York, NY (United States)
- Sponsoring Organization:
- European Union H2020; Gordon and Betty Moore Foundation; Hellman Fellowship; National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES)
- Grant/Contract Number:
- SC0019443
- OSTI ID:
- 1978664
- Journal Information:
- Nature Physics, Journal Name: Nature Physics Journal Issue: 1 Vol. 18; ISSN 1745-2473
- Publisher:
- Nature Publishing Group (NPG)Copyright Statement
- Country of Publication:
- United States
- Language:
- English
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