Two dimensional valley electrons and excitons in the noncentrosymmetric 3R MoS2

Possible control of the valley-dependent spin polarization in transition-metal dichalcogenides has been a hot topic as the valleytronics. Through the recent great progress based on the monolayer systems, people's interest is shifting to multilayered polytypes. The centrosymmetric 2H-stacked systems have been much studied for switching of the valley-dependent spin polarization. On the other hand, some of the authors [Suzuki et al., Nat. Nanotechnol. 9, 611 (2014)] have successfully fabricated the noncentrosymmetric 3R-stacked MoS2 multilayer and demonstrated the valley polarization independent of the number of layers. On the basis of this success, we further examined the valley electronic states in the 3R-MoS2 and found their novel two-dimensional properties utilizable for the valleytronics [Akashi et al., submitted.]. Namely, interlayer hopping of the valley electrons was proved to be zero as a consequence of a quantum-interference effect caused by the 3R-stacking geometry. In the talk, we report the results of the reflectivity measurement and analysis with an anisotropic hydrogen atomic model and show that the zero hopping causes 2D-hydrogen-like spectral series and confinement of the wave function within a single layer of the valley exciton.