Abstract
Two-dimensional semiconductors provide an ideal platform for exploration of linear exciton and polariton physics, primarily due to large exciton binding energy and strong light-matter coupling. These features, however, generically imply reduced exciton-exciton interactions, hindering the realization of active optical devices such as lasers or parametric oscillators. Here, we show that electrical injection of itinerant electrons into monolayer molybdenum diselenide allows us to overcome this limitation: dynamical screening of exciton-polaritons by electrons leads to the formation of new quasiparticles termed polaron-polaritons that exhibit unexpectedly strong interactions as well as optical amplification by Bose-enhanced polaron-electron scattering. To measure the nonlinear optical response, we carry out time-resolved pump-probe measurements and observe polaron-polariton interaction enhancement by a factor of 50 () as compared to exciton-polaritons. Concurrently, we measure a spectrally integrated transmission gain of the probe field of stemming from stimulated scattering of polaron-polaritons. We show theoretically that the nonequilibrium nature of optically excited quasiparticles favors a previously unexplored interaction mechanism stemming from a phase-space filling in the screening cloud, which provides an accurate explanation of the strong repulsive interactions observed experimentally. Our findings show that itinerant electron-exciton interactions provide an invaluable tool for electronic manipulation of optical properties, demonstrate a new mechanism for dramatically enhancing polariton-polariton interactions, and pave the way for realization of nonequilibrium polariton condensates.
3 More- Received 21 October 2019
- Revised 19 January 2020
- Accepted 19 February 2020
DOI:https://doi.org/10.1103/PhysRevX.10.021011
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
Material Makes Photons Bulky
Published 15 April 2020
Photons in certain materials can form large, strongly interacting quasiparticles, boosting nonlinear effects that could be useful in quantum optics.
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Popular Summary
van der Waals heterostructures constitute a new paradigm for electronics and photonics since they allow for combining, in a single structure, 2D materials with vastly different functionalities such as semiconductors, superconductors, insulators, and ferromagnets. However, a major limitation of this platform for quantum and nonlinear photonics has been the weakness of interactions between their elementary optical excitations. Here, we demonstrate how to overcome this limitation in an elegant and electrically controllable way.
In our experiments, we inject itinerant electrons into a monolayer of molybdenum diselenide. We find that interactions between these electrons and optically injected quasiparticles known as exciton-polaritons lead to the formation of new quasiparticles called polaron-polaritons. Because of their electronic screening cloud, these polaron-polaritons interact up to 50 times more strongly with each other than their excitonic counterparts.
Our results pave the way for the realization of nonlinear photonic devices based on van der Waals heterostructures with an electrically controlled interaction strength or optical gain. Concurrently, our experiments show how to realize a degenerate Bose-Fermi mixture composed of polaritons and electrons, which forms a starting point for the exploration of novel many-body physics in a nonequilibrium setting.