Giant Valley Coherence at Room Temperature in 3R WS_(2) with Broken Inversion Symmetry

Breaking the space-time symmetries in materials can markedly influence their electronic and optical properties.In 3R-stacked transition metal dichalcogenides,the explicitly broken inversion symmetry enables valley-contrasting Berry curvature and quantization of electronic angular momentum,providing an unprecedented platform for valleytronics.Here,we study the valley coherence of 3R WS_(2) large single-crystal with thicknesses ranging from monolayer to octalayer at room temperature.Our measurements demonstrate that both A and B excitons possess robust and thickness-independent valley coherence.The valley coherence of direct A(B)excitons can reach 0.742(0.653)with excitation conditions on resonance with it.Such giant and thickness-independent valley coherence of large single-crystal 3R WS_(2) at room temperature would provide a firm foundation for quantum manipulation of the valley degree of freedom and practical application of valleytronics.