Figure 4.

Layer-independent valley coherence under 2.33 eV excitation on resonance with the B exciton. (a) Linear-polarization-resolved PL spectra of 3R-stacked WS₂ from monolayer to pentalayer at room temperature. Red and black curves present copolarized configuration (incident light polarization e_i and scattered light polarization e_s are parallel to each other) and crosspolarized (incident light polarization and scattered light polarization are perpendicular to each other), respectively. Sharp peaks around B excitons are Raman peaks from the WS₂ and Si substrate. (b) Degree of valley coherence calculated from polarization-resolved PL spectra in (a). (c) Layer number (N)-dependent degree of linear polarization for B (magenta symbols), A (blue symbols), and I (red symbols) excitons. The distinct values within the same thickness are originated from different samples.