Observation of the Charge Density Wave Excitonic Order Parameter in Topological Insulator Monolayer WTe<sub>2</sub>.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 40906760.
- Also identified by DOI 10.1021/acsnano.5c08005 and PMC identifier 12445006.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Strong electron-hole interactions in a semimetal or narrow-gap semiconductor may drive a ground state of condensed excitons. Monolayer WTe<sub>2</sub> has been proposed as a host material for such an exciton condensate, but the order parameter─the key signature of a macroscopic quantum-coherent condensate─has not been observed. Here, we use Fourier-transform scanning tunneling spectroscopy (FT-STS) to study quasiparticle interference (QPI) and periodic modulations of the local density of states (LDOS) in monolayer WTe<sub>2</sub>. In WTe<sub>2</sub> on graphene, in which the carrier density can be varied via back-gating, FT-STS shows QPI features in the two-dimensional (2D) bulk bands, confirming the interacting nature of the bandgap in neutral WTe<sub>2</sub> and the semimetallic nature of highly n- and p-doped WTe<sub>2</sub>. We observe additional nondispersive spatial modulations in the LDOS imprinted on the topological edge mode of neutral WTe<sub>2</sub> on metallic substrates (graphene and graphite), which we interpret as the interaction of the topological edge mode with the expected charge density wave order parameter of the excitonic condensate in WTe<sub>2</sub> at low interaction strength due to screening by the metallic substrates.