Disorder-Induced Symmetry Breaking in Moiré Bands of Marginally Twisted Bilayer MoS₂.

Abstract

Twisted transition-metal dichalcogenides host highly tunable moiré potentials, flat bands, and correlated electronic phases, yet the role of disorder in shaping these emergent properties remains largely unresolved. Using scanning tunneling spectroscopy, we investigate the impact of electrostatic disorder on the electronic structure of marginally twisted (θ ≈ 0.95°) bilayer MoS₂. Differences of 15 meV in the onset energies of the valence and conduction bands between MX and XM stacked regions are observed and are unexpected in the presence of inversion symmetry. We also observe spatially correlated disorder in the onset energy that is consistent with a background random charge density of a few 10¹¹ cm^-2. Continuum model calculations for twisted MoS₂ show dramatic changes in the low-energy moiré bands in response to an electric displacement field, in quantitative agreement with experiment. Moreover, the calculated local density of states with disorder smearing compares well to experiment only when structural relaxation is accounted for. These results highlight the critical role of electrostatic disorder and structural relaxation in the electronic structure of moiré materials at the nanoscale.