Colloquium: Qihua Xiong

Title: Probing Light-Matter Interactions in Polar Semiconductor Nanomaterials

Speaker: Qihua Xiong   Nanyang Technological University

Place: Room 201, Building 12, Yuquan Campus

Time: 15:00-16:00, Thursday, May 24th

Abstract

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, scattering, spontaneous or stimulated emission, and second harmonic generation. In insulators or 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 (LO) phonon interactions in semiconductors. I will then present the resolved-sideband Raman cooling of LO phonons in semiconductors using ZnTe nanoribbon as a model system. The essential picture follows a similar physical picture of cavity optomechanics, whereby the LO phonon sidebands can be tuned to be in resonant with excitonic modes. Cooling or amplification of optical phonons can be realized by changing the detuning of pump laser. Next, I will introduce our latest work on room temperature exciton-polariton lasing in all-inorganic perovskite CsPbCl3 crystals embedded in optical microcavities. Those crystals have exceptionally large exciton binding energy, strong oscillator strength and can be grown by facile epitaxy-free techniques. Polariton lasing is 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. Our work suggests considerable promise of lead halide perovskites towards large-area, low-cost, high performance room temperature polariton devices and coherent light sources extending from the ultraviolet to near infrared range. The talk will be concluded by some progress of room temperature polariton condensate propagation in 1D perovskite microcavities, which exhibits ultrafast coherent propagation speed (~10 mm/ps) with great promise for ultrafast polaritonic devices and circuits.

References

1.   R. Su, et al., “Room temperature polariton lasing in all-inorganic perovskites”, Nano Lett. 17, 3982-3988 (2017)

2.   Q. Zhang, et al., “High quality whispering-gallery-mode lasing from cesium lead halide perovskite nanoplatelets”, Adv. Funct. Mater. 26, 6238-6245 (2016)

3.   J. Zhang, et al., “Resolved-sideband Raman Cooling of an Optical Phonon in Semiconductor Materials”, Nature Photonics 10, 600-605 (2016)

4.   S.T. Ha, et al., “Laser cooling of organic-inorganic lead halide perovskites”, Nature Photonics 10, 115–121 (2016)

About the Speaker 

Professor Qihua Xiong is both a professor at the School of Physical and Mathematical Sciences and the Electrical Engineering Department at Nanyang Technological University. In 1997, he graduated with his B.Sc. from Wuhan University’s School of Physics and Technology. In 2000, he received his M.Sc. from the Chinese Academy of Science’s Shanghai Institute of Atomic and Nuclear Physics (later renamed as the Shanghai Institute of Applied Physics). In 2006, under the advisement of Professor Peter C. Eklund, Professor Xiong obtained his Ph.D. from Penn State. From 2006 to 2009, Professor Xiong served as a post-doctoral researcher of Dr. Charles Lieber’s research group at Harvard University. In 2009, he was awarded financial support from the Singapore National Research Fund and joined as an assistant professor at Nanyang Technological University. In 2014, Professor Xiong was granted full tenure and became the Vice Dean of the School of Physical and Mathematical Sciences. By 2016, he was promoted to full professor. Professor Xiong’s main research specialty is experimental steady state and transient spectroscopy, which studies the interactions between light and matter. More specifically, his research investigates properties of low-dimensional semiconductor nanomaterials utilizing physical mechanisms of electron-photon-phonon coupling forces and quantum control. Professor Xiong has also conducted a series of influential works on the frontiers of physics in areas such as nano optics, surface plasmas, laser refrigeration, and optical properties of two-dimensional semiconductor materials. Professor Xiong has published more than 180 papers in many renowned international academic journals like Nature, Nano Letters, and Advanced Materials. Collectively, his papers have been cited more than 7,300 times with an h-index of 50. Professor Xiong’s research has also received awards and recognition from other world-renowned scientists. His accolades include the Singaporean Physics Society Nanoscience Prize (2015), the Singaporean National Research Fund Investigatorship Prize (2014), and the Nanyang Technological University’s Outstanding Research Award (2014).