Evidence for a monolayer excitonic insulator

Yanyu Jia, Pengjie Wang, Cheng Li Chiu, Zhida Song, Guo Yu, Berthold Jäck, Shiming Lei, Sebastian Klemenz, F. Alexandre Cevallos, Michael Onyszczak, Nadezhda Fishchenko, Xiaomeng Liu, Gelareh Farahi, Fang Xie, Yuanfeng Xu, Kenji Watanabe, Takashi Taniguchi, B. Andrei Bernevig, Robert J. Cava, Leslie M. SchoopAli Yazdani, Sanfeng Wu

Research output: Contribution to journalArticlepeer-review

70 Scopus citations


The interplay between topology and correlations can generate a variety of quantum phases, many of which remain to be explored. Recent advances have identified monolayer WTe2 as a promising material for doing so in a highly tunable fashion. The ground state of this two-dimensional crystal can be electrostatically tuned from a quantum spin Hall insulator to a superconductor. However, much remains unknown about the gap-opening mechanism of the insulating state. Here we report evidence that the quantum spin Hall insulator is also an excitonic insulator, arising from the spontaneous formation of electron–hole bound states, namely excitons. We reveal the presence of an intrinsic insulating state at the charge neutrality point in clean samples and confirm the correlated nature of this charge-neutral insulator by tunnelling spectroscopy. We provide evidence against alternative scenarios of a band insulator or a localized insulator and support the existence of an excitonic insulator phase in the clean limit. These observations lay the foundation for understanding a new class of correlated insulators with nontrivial topology and identify monolayer WTe2 as a promising candidate for exploring quantum phases of ground-state excitons.

Original languageEnglish (US)
Pages (from-to)87-93
Number of pages7
JournalNature Physics
Issue number1
StatePublished - Jan 2022

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy


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