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Friday, May 03, 2019
12:00 PM - 1:00 PM
East Bridge 114

IQIM Postdoctoral and Graduate Student Seminar

Room temperature photo-induced electron-hole gas-to-liquid transition in 2D materials
Alexander Kemper, Assistant Professor, Physics Department, North Carolina State University,

Abstract: In the 1960s it was observed that a sufficiently photoexcited semiconductor (Si) emits light at an unexpectedly high rate in cryogenic environments. This intense radiation was proposed by Keldysh (and later confirmed) to come from a high density, metallic, liquid formed by the excited electrons and the holes they left behind. It was subsequently observed in a variety of semiconductors at low temperatures, with the highest occurring in diamond (at ~165K). The critical temperature is set by the Coulomb interaction strength, which is typically strongly screened, leading to low critical temperatures.

However, two-dimensional materials have changed that. The poor screening of out-of-plane field lines lead to strong Coulomb interactions, large exciton binding energies, and a high temperature electron-hole liquid (EHL). The room temperature EHL was recently observed in MoS2 with photoluminescence experiments after modest photo-excitation. In this talk, I will present an overview of this new photoinduced phase of matter, including evidence for its existence, a theoretical phase diagram, and why it has not been seen before today.

References:

* Theoretical Phase Diagram for the Room-Temperature Electron-Hole Liquid in Photoexcited Quasi-Two-Dimensional Monolayer MoS2, Avinash Rustagi, Alexander F. Kemper, Nano Lett. 18, 1, 455-459.

* Dense Electron-Hole Plasma Formation and Ultra-Long Charge Lifetime in Monolayer MoS2 via Material Tuning, Alexander W. Bataller, Robert A. Younts, Avinash Rustagi, Yiling Yu, Hossein Ardekani, Alexander Kemper, Linyou Cao, and Kenan Gundogdu, Nano Lett. 2019, 19 (2), 1104–1111

For more information, please contact Marcia Brown by phone at 626-395-4013 or by email at marciab@caltech.edu.