报告题目：Probing Light-Matter Interactions in Polar Semiconductor Materials

报 告 人：Qihua Xiong，Professor of Physics and Electrical Engineering，Fellow, Singapore National Research Foundation；School of Physical and Mathematical Sciences，Nanyang Technological University

报告时间：2017-09-21 14:00

报告地点：物理系理科楼C302报告厅

报告摘要：The interaction of light with matter gives rises to a wide range of linear and nonlinear phenomena that we are familiar with, such as absorption and scattering, spontaneous or stimulated emission, and second harmonic generation. In polar semiconductors, the electromagnetic field of light polarizes the matter leading to the formation of elemental excitations such as excitons and exciton polaritons, due to long-range dipolar force as well as additional coupling to the optical fields. In this talk, I will first introduce the background of exciton, exciton polaritons and the electron/exciton-longitudinal optical phonon (LOP) interactions in semiconductors. I will then present the first fluorescence laser cooling of semiconductors based on cadmium sulfide nanoribbons, enabled by enhanced strong exciton-LOP coupling at nanoscale. In zinc telluride nanoribbons, resolved-sideband Raman cooling of LOPs can be realized with a similar physical picture of cavity optomechanics, in which the excitonic mode was utilized to assist the photoelastic Raman scattering from the LOPs. By detuning the laser pumping, the dipole oscillation of the LOPs is photoelastically attenuated (enhanced) to a colder (hotter) state, corresponding to the laser cooling of amplification of the LOPs respectively. Finally, I will introduce our recent work on strong light-matter coupling in all-inorganic perovskite crystals embedded in optical microcavities. Those prototype semiconductors have exceptionally large exciton binding energy, strong oscillator strength and facile epitaxy-free growth. Room temperature exciton polariton lasing can be realized, which was unambiguously evidenced by a superlinear power dependence, macroscopic ground state occupation, blueshift of ground state emission, and the build-up of long-range spatial coherence, suggesting considerable promise of room temperature polariton devices and coherent light sources extending from the ultraviolet to near infrared range. Future work will be briefly discussed, with a particular interest on transient spectroscopy investigations of semiconductors.