Robust Layer-Dependent Valley Polarization and Valley Coherence in Spiral WS2 at Room Temperature

In the emerging field of valleytronics, it is aimed to coherently manipulate the valley pseudospin as an information-bearing degree of freedom. The 2D transition-metal dichalcogenides (TMDCs) provide a unique possibility to generate an excitonic valley pseudospin, opening the way to valley information. Although significant development of valley pseudospin in layered materials has been achieved recently, looking for new TMDCs featuring robust valley phenomenon at room temperature is still desirable for practical applications. Herein, the valley pseudospin of the spiral WS2 with different layer thicknesses at room temperature is investigated by both circular and linear polarization-resolved photoluminescence spectroscopy. In the experimental results, it is demonstrated that the spiral WS2 emerges robust valley polarization and valley coherence, the degree of circular polarization, and linear polarization gradually increase with the lift of the layer thicknesses, reaching up to 0.91 for valley polarization and 0.94 for valley coherence, respectively. The robust layer-dependent valley pseudospin may originate from the intrinsic broken inversion symmetry, due to the spiral structure of the multilayer WS2. The robust and near-unity valley polarization and valley coherence at room temperature in the spiral WS2 may provide a new platform for optical manipulation of the valley pseudospin for further valleytronics applications.