biostudies-literatureWatson LUniversidad Aut?noma de MadridCentre of Excellence in Future Low-Energy Electronics Technologies, Australian Research CouncilNational Research Foundation SingaporeMinistry of Education - SingaporeAgencia Estatal de Investigaci?nHORIZON EUROPE Marie Sklodowska-Curie ActionsAustralian Research Council32374-32381https://www.ebi.ac.uk/biostudies/studies/S-EPMC12445006biostudies-literatureUnknown19(36)Strong electron-hole interactions in a semimetal or narrow-gap semiconductor may drive a ground state of condensed excitons. Monolayer WTe₂ 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 WTe₂. In WTe₂ 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 WTe₂ and the semimetallic nature of highly n- and p-doped WTe₂. We observe additional nondispersive spatial modulations in the LDOS imprinted on the topological edge mode of neutral WTe₂ 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 WTe₂ at low interaction strength due to screening by the metallic substrates.ACS nanoObservation of the Charge Density Wave Excitonic Order Parameter in Topological Insulator Monolayer WTe<sub>2</sub>.PMC12445006101063547CEX2020001039-SCEX2018000805- MCNS2022-135175FT2201000290PID2021-123776NB-C21NRF-CRP21-2018-0001RYC2020-029317- ICE170100039MOE-MOET32023-0003Garnica MDi Bernardo IPapaj MTong ZWatson LEdmonds MTWeber BFuhrer MSQue YVazquez de Parga ALLin HMukherjee SRipoll JKumar AChan YHfalseObservation of the Charge Density Wave Excitonic Order Parameter in Topological Insulator Monolayer WTe<sub>2</sub>.Strong electron-hole interactions in a semimetal or narrow-gap semiconductor may drive a ground state of condensed excitons. Monolayer WTe₂ 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 WTe₂. In WTe₂ 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 WTe₂ and the semimetallic nature of highly n- and p-doped WTe₂. We observe additional nondispersive spatial modulations in the LDOS imprinted on the topological edge mode of neutral WTe₂ 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 WTe₂ at low interaction strength due to screening by the metallic substrates.2025-01-01T00:00:00Z2025 Sep2026-06-03T15:28:00.882Z2026-04-29T03:12:27.709ZS-EPMC124450064090676010.1021/acsnano.5c08005