On Oct. 16, 2014, Prof. Xiaodong Cui from School of physics, HongKong University visited SINANO and delivered a talk entitled “Optical properties of 2D transition metal dichalcogenides”. The presentation was chaired by Prof. Liwei Chen, the deputy director of SINANO. Researchers and graduated students attended the lecture.  

  The ultimate goal of making electronic devices with atomically thin layers stimulates the research in layered materials, in particular the Group VI transition metal dichalcogenides (TMDs). Prof. Cui presented recent progress of his group by optical method to prove that the TMDs nanosheets come across a transition from indirect gap materials at the bulk form to direct band gap semiconductors at the monolayer limit. In addition, with the photoluminescence property of the material, they proved the characteristic inversion symmetry breaking presented in monolayer TMDs leads to non-zero Berry curvatures and opposite orbit magnetic moments at K/K’ valleys located at the six corners of the first Brillouin zone. These features provide the opportunity to manipulate electrons’ additional internal degrees of freedom, namely the valley degree of freedom, making monolayer TMDs a promising candidate for the conceptual valleytronics. Thorough discussion on the impressive results was carried out after presentation.