Observation 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 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.
Authors
- Yande Que (ORCID: https://orcid.org/0000-0002-5267-4985)
- Yang‐Hao Chan (ORCID: https://orcid.org/0000-0002-9113-5319)
- Hsin Lin (ORCID: https://orcid.org/0000-0002-4688-2315)
- Iolanda Di Bernardo (ORCID: https://orcid.org/0000-0002-2364-5544)
- Amadeo L. Vázquez de Parga (ORCID: https://orcid.org/0000-0003-0551-1603)
- Bent Weber (ORCID: https://orcid.org/0000-0001-8586-127X)
- Manuela Garnica (ORCID: https://orcid.org/0000-0002-7861-9490)
- Mark T. Edmonds (ORCID: https://orcid.org/0000-0001-8054-5470)
- Zhengjue Tong (ORCID: https://orcid.org/0000-0002-2805-5316)
- Liam Watson (ORCID: https://orcid.org/0000-0002-8334-2465)
- Michael S. Fuhrer (ORCID: https://orcid.org/0000-0001-6183-2773)
- Shantanu Mukherjee (ORCID: https://orcid.org/0000-0002-4927-5131)
- Michał Papaj (ORCID: https://orcid.org/0000-0002-3127-6558)
- Joan Ripoll
- Amit Kumar (ORCID: https://orcid.org/0009-0007-9070-3218)
Institutions
- Madrid Institute for Advanced Studies (ES)
- Nanyang Technological University (SG)
- Indian Institute of Technology Madras (IN)
- Australian Regenerative Medicine Institute (AU)
- Quantum Diamond Technologies (United States) (US)
- ARC Centre of Excellence in Future Low-Energy Electronics Technologies (AU)
- Diamond Materials (United States) (US)
- Institute of Physics, Academia Sinica (TW)
- Yukhnovskii Institute for Condensed Matter Physics of the National Academy of Sciences of Ukraine (UA)
- Materials Design (France) (FR)
- Institute of Atomic and Molecular Sciences, Academia Sinica (TW)
- Institute of Chemistry, Academia Sinica (TW)
- University of Houston (US)
- Monash University (AU)
- Universidad Autónoma de Madrid (ES)
- Academia Sinica (TW)
Publication Details
- Journal
- ACS Nano
- Published
- 2025-09-04
- DOI
- https://doi.org/10.1021/acsnano.5c08005
- Citations
- 1
- Primary Topic
- Topological Materials and Phenomena
- Type
- article
- Field-Weighted Citation Impact
- 1.25
Funders
- National Research Foundation
- National Research Foundation Singapore
- Ministry of Education - Singapore
- Ministry of Education, India
- Universidad Autónoma de Madrid
- Ministerio de Ciencia e Innovación
- Bộ Giáo dục và Ðào tạo
- Australian Research Council
- Agencia Estatal de Investigación
- Centre of Excellence in Future Low-Energy Electronics Technologies, Australian Research Council
- HORIZON EUROPE Marie Sklodowska-Curie Actions