Coulomb interactions among electrons and holes in two-dimensional (2D) semimetals with overlapping valence and conduction bands can give rise to a correlated insulating ground state via exciton formation and condensation. One candidate material in which such excitonic state uniquely combines with non-trivial band topology are atomic monolayers of tungsten ditelluride (WTe2), in which a 2D topological excitonic insulator (2D TEI) forms. However, the detailed mechanism of the 2D bulk gap formation in WTe2, in particular with regard to the role of Coulomb interactions, has remained a subject of ongoing debate. Here, we show that WTe2 is susceptible to a gate-tunable quantum phase transition, evident from an abrupt collapse of its 2D bulk energy gap upon ambipolar field-effect doping. Such gate tunability of a 2D TEI, into either n- and p-type semimetals, promises novel handles of control over non-trivial 2D superconductivity with excitonic pairing.
@article{arxiv.2309.16260,
title = {A gate-tunable quantum phase transition in a topological excitonic insulator},
author = {Yande Que and Yang-Hao Chan and Junxiang Jia and Anirban Das and Zhengjue Tong and Yu-Tzu Chang and Zhenhao Cui and Amit Kumar and Gagandeep Singh and Hsin Lin and Shantanu Mukherjee and Bent Weber},
journal= {arXiv preprint arXiv:2309.16260},
year = {2023}
}