The interaction of light with matter gives rises to a wide range of phenomena that we are familiar with, such as absorption, scattering, and spontaneous or stimulated emission. The electromagnetic field of light polarizes the matter that is responsible for many linear or nonlinear optical processes, which lay down the foundation of a wide range of photonic and optoelectronic devices that have modernized our life and society. In this talk, I will first introduce our capability of probing light-matter interactions in nanoscale semiconductor materials, whereby the quantum size and structure anisotropy play an important role. I will then present the first laser cooling of semiconductors based on cadmium sulfide nanoribbons and inorganic-organic perovskites crystals, enabled by strong exciton-longitudinal optical (LO) phonon coupling at nanoscale, giving rise to considerable promise in optical refrigeration applications. In zinc telluride nanoribbons, resolved-sideband Raman cooling of specific optical phonon modes can be realized with a similar physical picture of cavity optomechanics, whereby the LO phonon sidebands can be tuned to be in resonant with excitons. Cooling or amplification of optical phonons can be realized by changing the detuning of pump laser. Finally, I will introduce our work on interlayer coupling and charge transfer in 2D atomically thin semiconductors and their heterostructures. The unique charge transfer mechanism in 2D semiconductor heterostructures leads to an interesting blinking phenomenon, whereby a bright state emission occurs in one monolayer while a dark state emission occurs in the other, and vice versa. Such correlated blinking can be probed in detail by steady-state and transient spectroscopy measurements, providing new platform to study the long-standing puzzling blinking phenomenon in nanomaterials.

References:

1. W.G. Xu, W.W. Liu, J. F. Schmidt, W.J. Zhao, X. Lu, T. Raab, C. Diederichs, W.B. Gao, D. V. Seletskiy, and Q.H. Xiong, “Correlated fluorescence blinking in two-dimensional semiconductor heterostructures”, Nature, Doi:10.1038/nature20601 (2017)
2. J. Zhang, Q. Zhang, X.Z. Wang, L.C. Kwek and Q.H. Xiong, “Resolved-sideband Raman Cooling of an Optical Phonon in Semiconductor Materials”, Nature Photonics 10, 600-605 (2016)
3. S.T. Ha, C. Shen, J. Zhang and Q.H. Xiong, “Laser Cooling of Organic-inorganic Lead Halide Perovskites”, Nature Photonics 10, 115–121 (2016)
4. J. Zhang, D.H. Li, R.J. Chen and Q.H. Xiong, “Laser Cooling of a Semiconductor by 40 Kelvin”, Nature 493, 504-508 (2013) (Cover Highlight, highlighted by Nature Photonics in its April and May issues)
5. Y.Y. Zhao, X. Luo, H. Li, J. Zhang, P.T. Araujo, C.K. Gan, J. Wu, H. Zhang, S.Y. Quek, M.S. Dresselhaus, and Q.H. Xiong, “Interlayer breathing and shear modes in few-trilayer MoS₂ and WSe₂”, Nano Lett. 13, 1007-1015 (2013)

Qihua Xiong received his B.S. degree in physics from Wuhan University in 1997, and then finished three years graduate studies at the Shanghai Institute of Applied Physics, Chinese Academy of Sciences. He went to the United States in 2000 and received Ph.D. degree under the supervision of Prof. Peter C. Eklund from The Pennsylvania State University in 2006. After three years postdoctoral experience in Prof. Charles M. Lieber’s group at Harvard University, he joined Nanyang Technological University as an assistant professor in 2009 and promoted to Nanyang Associate Professor in 2014. He was promoted to full Professor in 2016 recently. He is a Fellow of Singapore National Research Foundation awarded in 2009 and the inaugural NRF Investigatorship Award by Singapore National Research Foundation. He is the recipient of IPS Nanotechnology Physics Award (2015) and Nanyang Award for Research Excellence of NTU (2014). Prof. Xiong’s research focuses on light-matter interactions of emergent quantum matter by optical spectroscopy approaches. He recently ventured into the field of 2D layered materials and laser cooling of solids.