Abstract:

In this talk, I will introduce two pieces of work in two-dimensional layered materials done in our group. In the first one, we report an unusual valley polarization (VP) up to 70% for B exciton in monolayer MoSe2, while that for A exciton is less than 3%, and a small but finite negative VP for A- trion. These results reveal several new intra- and inter-valley scattering processes which significantly affect valley polarization. The second one is the observation of an ultralow-frequency collective compression mode (CCM) in atomically thin black phosphorus (BP). This novel CCM indicates an unusually strong interlayer coupling in BP, which is quantitatively supported by a phonon frequency analysis and first-principles calculations. The CCM and another branch of low-frequency Raman modes shift sensitively with changing number of layers, allowing an accurate determination of the thickness up to tens of atomic layers. These results offer fundamental insights and practical tools for exploring multilayer BP in new device applications.
 
 
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