Dependence of the exciton energies in WSe 2 /WSe 2 bilayer structures on the twisting angle

The discovery of two-dimensional materials has revolutionized condensed matter physics, with transition metal dichalcogenides (TMDCs) offering tunable electronic and optical properties. Monolayer tungsten diselenide WSe 2 , a direct bandgap semiconductor with strong excitonic effects, is especially promising for optoelectronics. When two WSe 2 monolayers are stacked with controlled twisting angles, the resulting twisted bilayer (tB) material forms a moiré superlattice that significantly modifies its electronic structure and optical response through interlayer coupling and band reconstruction. In a systematic study employing photoluminescence (PL) and differential micro-reflectance contrast ( μ RC) spectroscopy and supported by first-principles calculations, we investigate the optical properties of tB WSe 2 for twisting angles 0 ∘ < θ < 60 ∘ . Excitonic peaks (A, B, C, D) exhibit angle-dependent energy shifts. Notably, A and C excitons show characteristic energy splittings that reflect twisting-angle-modulated interlayer hybridization and spin–orbit coupling effects. The A exciton shows local minima at 0 ∘ and 60 ∘ , and a maximum near 30 ∘ . This pattern reflects variations in interlayer hybridization—stronger coupling at 0 ∘ and 60 ∘ , weaker at intermediate angles—consistent with moiré-induced modifications. Our work reveals the periodic modulation of exciton energies in WSe 2 homo-bilayers across a wide range of twisting angles, directly linking these variations to interlayer coupling strength and spin–orbit splitting. Our findings provide clear experimental–theoretical consistency, identifying the twisting angle as an effective tuning knob for excitonic transitions and interlayer interactions in TMDC bilayers. The work contributes to the understanding of the structure–property relationships in twisted TMDC materials, and the results may lead to new design principles for next-generation, moiré-engineered optoelectronic and quantum devices.