CM In the literature: contested

Is the insulating state of monolayer WTe2 an excitonic insulator

In plain words

Monolayer WTe2 is insulating at charge neutrality and conducts along its edges. Experiments suggest the bulk gap comes from electron-hole pairing, but a gap from ordinary band mixing or disorder has not been ruled out.

Precise statement

Monolayer 1T'-WTe2 has a small bulk gap at charge neutrality that closes with gate-induced doping; 2022 experiments interpreted it as an interaction-driven excitonic insulator, possibly with spontaneous symmetry breaking. Determine whether the gap is an excitonic condensate (order parameter, symmetry breaking, mean-field or BKT-like temperature dependence, collective mode) or a single-particle hybridization gap enhanced by interactions. An answer is the identified gap origin with evidence for or against a broken symmetry.

What would settle it

Direct detection of the predicted broken symmetry (e.g. by optical second-harmonic generation or scanning tunneling spectroscopy of order-parameter domains) or of an excitonic collective mode.

Status in the literature

Unverified note

2022 Nature Physics reports gave excitonic signatures; independent evidence of a broken symmetry had not appeared as of 2025.