Following the success of graphene, the transition metal dichalcogenide (TMDC) family in the form of MX2 (M = Mo, W; X = S, Se, Te) has attracted great attention as a two-dimensional semiconductor. In particular, the band gap of TMDCs transitions from the indirect type to direct type at the monolayer limit, giving rise to an extraordinarily strong light-matter interaction. In this talk, I will discuss the physics behind the optical response of TMDCs and our effort to harness it. We will present our discovery of a strong and anomalous excitonic effect in the TMDC monolayer. The room-temperature stable exciton stems from an unscreened Coulomb interaction in the two-dimensional space. Also, we will report our recent success on the coherent manipulation of the valley polarization, which is a degree of freedom analogous to spin but exists in the momentum space of the electron. The ability to control the valley degree of freedom might enable a new platform for quantum information applications.
Dr Ziliang Ye studied Physics for BSc at Fudan University in Shanghai. In 2008, Dr Ye moved to the United States to pursue PhD at UC Berkeley with Prof Xiang Zhang, in the graduate program of applied science and technology. After receiving PhD in 2013, he joined Prof Tony Heinz’s group at Columbia University, and later on at Stanford University, in the applied physics department. Dr Ye’s research topics include plasmonics, metamaterials, nearfield optics, and 2D materials. He is currently focused on studying the 2D semiconductor physics using ultrafast optical pulses. Dr Ye has received multiple national awards including MRS gold medalist, Kavli nanoscience institute thesis prize, and Chinese government award for outstanding student aboard.