Observation of the Charge Density Wave Excitonic Order Parameter in Topological Insulator Monolayer WTe 2

作者：Liam Watson, Joan Ripoll, Zhengjue Tong, Amit Kumar, Yande Que, Yang‐Hao Chan, Hsin Lin, Shantanu Mukherjee, Manuela Garnica, Mark T. Edmonds, Michał Papaj, Amadeo L. Vázquez de Parga, Bent Weber, Iolanda Di Bernardo, Michael S. Fuhrer · 发表于：ACS Nano · 年份：2025 · DOI：10.1021/acsnano.5c08005 · 被引用次数：4 · 研究领域：Topological Materials and Phenomena、2D Materials and Applications、Quantum and electron transport phenomena

High Resolution Image Download MS PowerPoint Slide Strong electron–hole interactions in a semimetal or narrow-gap semiconductor may drive a ground state of condensed excitons. Monolayer WTe 2 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 2 . In WTe 2 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 2 and the semimetallic nature of highly n- and p-doped WTe 2 . We observe additional nondispersive spatial modulations in the LDOS imprinted on the topological edge mode of neutral WTe 2 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 2 at low interaction strength due to screening by the metallic substrates.