Title：Probing Light-Matter Interactions in Polar Semiconductor Nanomaterials

Reporter：Qihua Xiong   Nanyang Technological University

Place： Teaching Building 12-201

Time： May 24，15:00-16:00

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 m/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)

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