Giant Modulation of Interlayer Coupling in Twisted Bilayer ReS<sub>2</sub>.

Abstract

Stacking monolayers of two-dimensional (2D) transition metal dichalcogenides with different twist angles can provide a way to tune their quantum optical and electronic characteristics. This study demonstrates that the bandgap energy and interlayer coupling strength of twisted bilayer (tBL) ReS₂ can be continuously modulated by the twist angle. By controlling the twist angle between 0° and 10°, the exciton energy of tBL ReS₂ is tuned over a range of 40 meV, which is comparable to the difference between the exciton energies of intrinsic monolayer and bilayer ReS₂. Such a wide modulation range for the interlayer coupling strength of tBL ReS₂, which significantly affects the band structure, is also shown by the systematic shift in the low-and high-frequency Raman modes and results of a strain study using scanning transmission electron microscopy imaging. Density functional theory calculations on moiré superlattice tBL ReS₂ structures confirm a consistent increase in the bandgap with the twist angle. The strong modulation of interlayer coupling by the twist angle in tBL ReS₂ is attributed to the low symmetry of the 1T' structure and in-plane anisotropy of the ReS₂ lattice. These findings demonstrate the enhanced tunability of twist-controlled electronic structure in anisotropic 2D materials, offering new pathways for designing reconfigurable quantum materials.