报告时间:   2016年8月22日（星期一）

报告内容:

Photonic quantum computer, quantum communication, quantum metrology and quantum optical technologies rely on the single-photon source (SPS). However, the SPS with valley-polarization remains elusive and the tunability of magneto-optical transition frequency and emission/absorption intensity is restricted, in spite of being highly in demand for valleytronic applications. Here we report a new class of SPSs based on carriers spatially localized in two-dimensional monolayer transition metal dichalcogenide quantum dots (QDs). We demonstrate that the photons are absorbed (or emitted) in the QDs with distinct energy but definite valley-polarization. The spin-coupled valley-polarization is invariant under either spatial or magnetic quantum quantization. However, the magneto-optical absorption peaks undergo a blue shift as the quantization is enhanced. Moreover, the absorption spectrum pattern changes considerably with a variation of Fermi energy. This together with the controllability of absorption spectrum by spatial and magnetic quantizations, offers the possibility of tuning the magneto-optical properties at will, subject to the robust spin-coupled valley polarization.

I am also going to present a theory to describe the momentum-dependent exciton spectrum of monolayer molybdenum disulfide. We find that although monolayer MoS2 is a direct-gap semiconductor when classified by its quasiparticle band structure it may well be an indirect gap material when classified by its excitation spectra. We speculate on the role of this property in luminescence characteristics.

个人简介:

Dr. Qu  received his PhD in condensed matter theory in 1998 from University of Brasilia. Then he did his postdoctoral research in National Research Council of Canada, Ottawa.  After that as a visiting professor, he worked at University of South California Berkeley, University of Texas at Austin and International Center for Theoretical Physics (ICTP), Italy, respectively. Now, he worked in Institute of Physics and International Cernter for Condensed Matter Physics as professor. His research focuses on many-body effects, quantum spintronics, magnetotronics and valleytronics in low dimensional systems. The current research interest of Qu’s group is on nanodevices, electronic structure, exciton physics, valley and spin physics in atomically thin 2D materials and their heterostructures.