Evidence for a monolayer excitonic insulator

By Yanyu Jia, Pengjie Wang, Cheng-Li Chiu, Zhida Song, Guo Yu, Berthold Jäck, Shiming Lei, S. Klemenz, F. A. Cevallos, Michael Onyszczak and 12 more. Nature Physics, 2020

178 citations recorded by the source corpus.

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 WTe 2 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 WTe 2 as a promising candidate for exploring quantum phases of ground-state excitons. Insulating states that are formed because of pairing between electrons and holes are known to exist in engineered bilayer structures in high magnetic fields. Now evidence suggests they can occur in a monolayer crystal at zero field.

Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/38a9cdc6ad2615453af9579d9a9a8523b9b401af

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In Atomic and Molecular Physics, and Optics

1. P. Törmä
2. S. Peotta
3. Bogdan Andrei Bernevig
4. Peter Kuchment
5. Luis E. F. Foa Torres
6. M. Aidelsburger

In Materials Chemistry

1. Bogdan Andrei Bernevig
2. P. Törmä
3. S. Peotta

Citations in the corpus

• Superconductivity, superfluidity and quantum geometry in twisted multilayer systems (2021, background): “Another promising moiré material is WTe2, where a topological exciton insulator has been observed in single layer [143] but where metallic behavior is obtained in moiré bilayers [144]; the appearance of superconductivity at some twist angles in WTe2 would be interesting due to its topological bands.”