Polariton-electron interactions in two dimensional materials (Prof. Atac Imamoglu)

Polariton-electron interactions in two dimensional materials

  • Date: Jan 7, 2020
  • Time: 14:30
  • Speaker: Prof. Atac Imamoglu
  • ETH Zürich, Switzerland
  • Location: Max Planck Institute of Quantum Optics
  • Room: Herbert Walther Lecture Hall
  • Host: MCQST-Kolloquium
Two dimensional materials provide new avenues for synthesizing compound quantum systems. Monolayers with vastly different electric, magnetic or optical properties can be combined in van der Waals heterostructures which ensure the emergence of new functionalities; arguably, the most spectacular example to date is the observation of strong correlations and low electron density superconductivity in Moire superlattices obtained by stacking two monolayers with a finite twist angle.

Optically active monolayers such as molybdenum diselenide provide a different "twist" as they allow for investigation of nonequilibrium dynamics in van der Waals heterostructures by means of femtosecond pump-probe measurements. Moreover, interactions between electrons and the elementary optical excitations such as excitons or polaritons, provide an ideal platform for investigation of quantum impurity physics, with possibilities to probe both Fermi- and Bose-polaron physics as well as mixtures with tunable density of degenerate fermions and bosons.

After introducing the framework we use to describe many-body optical excitations in van der Waals heterostructures, I will describe two recent developments in the field. The first experiment uses pump-probe measurements to demonstrate how exciton-electron interactions lead to strong enhancement of polaritonpolariton interactions, as well as to optical gain by stimulated cooling of exciton-polaron-polaritons. The second experiment shows that a tri-layer system, consisting of two semiconducting monolayers separated by an insulating layer, could lead to hybridization of intra- and inter-layer excitons. The latter has potential applications ranging from strongly interacting polaritons to enhancing exciton-mediated electron-electron attractive interactions.

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