Nano-ARPES investigation of structural relaxation in small angle twisted bilayer tungsten disulfide

The diverse and intriguing phenomena observed in twisted bilayer systems, such as graphene and transition-metal dichalcogenides, prompted new questions about the emergent effects that they may host. However, the practical challenge of realizing these structures on a scale large enough for spectroscopic investigation, remains a significant hurdle, resulting in a scarcity of direct measurements of the electronic band structure of twisted transition metal dichalcogenide bilayers. Here, we present a systematic nanoscale angle-resolved photoemission spectroscopy investigation of bulk, single-layer, and twisted bilayer $\mathrm{W}{\mathrm{S}}_{2}$ with a small twist angle of $4.{4}^{\ensuremath{\circ}}$. The experimental results are compared with theoretical calculations based on density functional theory along the high-symmetry directions $\overline{\mathrm{\ensuremath{\Gamma}}}\text{\ensuremath{-}}\overline{\mathrm{K}}$ and $\overline{\mathrm{\ensuremath{\Gamma}}}\text{\ensuremath{-}}\overline{\mathrm{M}}$. Surprisingly, the electronic band structure measurements suggest a structural relaxation occurring at $4.{4}^{\ensuremath{\circ}}$ twist angle and the formation of large, untwisted bilayer regions replacing most of the twisted area.