Imaging moir\'e flat bands and Wigner molecular crystals in twisted bilayer MoTe2

TL;DR

This study uses STM/STS to explore the electronic structure of twisted bilayer MoTe2, revealing topological flat bands, electric-field-induced topological transitions, and the emergence of Wigner molecular crystals, advancing understanding of moiré quantum phenomena.

Contribution

It provides a microscopic understanding of topological flat bands and correlated phases in tMoTe2, demonstrating electric-field control over topology and electron ordering.

Findings

Identification of localized flat bands in moiré superlattice regions.

Observation of topological transition driven by electric field.

Detection of Wigner molecular crystals at specific moiré fillings.

Abstract

Two-dimensional semiconducting moir\'e materials have emerged as a highly tunable platform for exploring novel quantum phenomena. Recently, tMoTe2 has attracted significant attentions due to the observation of the long-sought fractional quantum anomalous Hall effect. However, a comprehensive microscopic understanding of the tMoTe2 moir\'e superlattice remains elusive. Here, we report STM/STS studies in dual-gated tMoTe2 moir\'e devices with twist angles ranging from 2.3 to 3.8 deg. The device consists of two independent back-gates, one enables an ohmic contact for tMoTe2, while the other fine-tunes the Fermi level of tMoTe2. This dual-gate control enables direct measurement of the electronic structure in tMoTe2 under varied displacement fields and moir\'e filling factors, by fine tuning the gate voltage and the tip bias. Our STS spectra and spatial imaging reveal that the low-energy moir\'e flat bands are predominantly localized in the XM and MX regions of the moir\'e superlattice. At zero E-field, these bands form a honeycomb lattice with non-trivial topology, whereas an applied E-field drives a transition into two distinct triangular lattices with trivial topology. The spatial distributions align with large-scale first-principle calculations, demonstrating that the topological flat bands arise from the K-valley hybridization between the top and bottom MoTe2 layers. Furthermore, we show that the effective moir\'e potential depth can be controlled via gate and tip biases. At sufficient potential depths, we observe the emergence of Wigner molecular crystals, transitioning MX triangular lattice into a Kagome lattice at MX moir\'e filling factor 3. These results elucidate the microscopic origin of topological flat bands in tMoTe2 and demonstrate electric-field control of topology and correlated electronic orders, paving the way to engineer exotic quantum phases in moir\'e simulators.