Transition metal dichalcogenide homobilayers unite two frontiers of quantum materials research: sliding ferroelectricity, arising from rhombohedral (R) stacking, and moir\'e quantum matter, emerging from small-angle twisting. The spontaneous polarization of ferroelectric R-stacked homobilayers produces a highly tunable band structure, which, together with strain-induced piezoelectricity, governs the topology and correlated electronic phases of twisted bilayers. Here we present a systematic low-temperature optical spectroscopy study of R-stacked bilayer WSe2 to quantitatively establish its fundamental electronic and ferroelectric properties. Exciton and exciton-polaron spectroscopy under doping reveals a pronounced electron-hole asymmetry that confirms type-II band alignment, with the conduction and valence band edges located at the Λ and K valleys, respectively. Through distinct excitonic responses and tunable interlayer-intralayer exciton hybridization under displacement fields, we uncover the coexistence of AB and BA ferroelectric domains. Using exciton-polarons as a probe, we directly measure the intrinsic polarization field and extract the interlayer potential. Finally, we demonstrate electric-field-driven symmetric switching of the valence band maximum, attributed to ferroelectric domain switching. These results provide a complete experimental picture of the band alignment, spontaneous polarization field, and domain dynamics of R-stacked WSe2, establishing key parameters to understand twisted bilayers and enabling new ferroelectric and excitonic device opportunities.
@article{arxiv.2509.02886,
title = {Highly tunable band structure in ferroelectric R-stacked bilayer WSe$_2$},
author = {Zhe Li and Prokhor Thor and George Kourmoulakis and Tatyana V. Ivanova and Takashi Taniguchi and Kenji Watanabe and Hongyi Yu and Mauro Brotons-Gisbert and Brian D. Gerardot},
journal= {arXiv preprint arXiv:2509.02886},
year = {2025}
}