Tuning commensurability in twisted van der Waals bilayers
Abstract: Moiré superlattices in van der Waals bilayers, created at small twist angles (θt), result in long-wavelength patterns with approximate translational symmetry. Small angle twisted transition metal dichalcogenide (TMD) homobilayers have emerged as an ideal platform for investigating strong correlation phenomena, highlighted by recent discoveries of fractional Chern insulator (FCI) states in twisted MoTe2, Chern insulators (CI), and unconventional superconductivity in twisted WSe2. However, at large twist angles, moiré patterns are incommensurate, except at certain discrete angles. Utilizing valley-resolved scanning tunneling spectroscopy (STS), we explore various behaviors of bilayer WSe2 as the twist angle is tuned from small to large, spanning nearly commensurate to commensurate and incommensurate regimes. At small twist angles, we observe skyrmion textures in the layer degree of freedom within rhombohedral-stacked (R-stacked) twisted WSe2 homobilayers. For large angles, we identify the formation of incommensurate dodecagon quasicrystals at θt = 30° and commensurate moiré crystals at θt = 21.8°, where mutual Umklapp scatterings and coherent couplings are investigated. Additionally, near large commensurate angles, we uncover the spontaneous formation of a super-moiré structure in twisted bilayers, characterized by a periodic arrangement of three inequivalent commensurate stacking configurations. Our findings not only highlight valley-resolved STS as a crucial technique for studying twisted bilayer TMDs but also establish novel platforms for advancing twistronics of the moiré TMDs.
About the QSQM: The EFRC-QSQM center aims to develop and apply nontrivial quantum sensing to measure and correlate local and nonlocal quantum observables in exotic superconductors, topological crystalline insulators, and strange metals. The center is led by the University of Illinois at Urbana-Champaign in partnership with the University of Illinois at Chicago and the SLAC National Accelerator Laboratory.
