[MOS] TODAY - Modern Optics and Spectroscopy Seminar with Xiaoyang Zhu (Columbia University)

[Christine Brooks]

There will be a Modern Optics and Spectroscopy Seminar held today at 12pm in 5-234

**Please note updated location**

Xiaoyang Zhu
Columbia University

“Ferroelectric polarons and spectroscopic view of the “perfect” semiconductor”

Lead halide perovskites have been demonstrated as high performance materials in solar cells and light-emitting devices. These materials are characterized by coherent band transport expected from crystalline semiconductors, but dielectric responses and phonon dynamics typical of liquids. Here we explain the essential physics in this class of materials based their dielectric functions and dynamic symmetry breaking on nano scales. We show that the dielectric function in the THz region may lead to dynamic and local ordering of polar nano domains by an extra electron or hole, resulting a quasiparticle which we call a ferroelectric large polaron, a concept similar to solvation in chemistry. Compared to a conventional large polaron, the collective nature of polarization in a ferroelectric large polaron may give rise to order(s)-of-magnitude larger reduction in the Coulomb potential. Using two-dimensional optical Kerr effect (2D-OKE) spectroscopy, we directly probe the energetics and local phonon responses of ferroelectric polarons. The ferroelectric polaron may explain the defect tolerance and low recombination rates of charge carriers in lead halide perovskites, as well as providing a design principle for the “perfect” semiconductor for optoelectronics.


Refreshments will be served immediately following the seminar!


Christine Brooks
Administrative Assistant
Massachusetts Institute of Technology
Department of Chemistry
77 Massachusetts Ave, 6-333
Cambridge, MA 02139
p: 617.253.7239
e: cbrooks at mit.edu<mailto:cbrooks at mit.edu>

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