Programme

I.6 -- Invited, VCTP-47

Date: Monday, 1 August 2022

Time: 16:30 - 17:00

Online presentation

Strong coupling regime between a non-Hermitian topological charge and excitons in semiconductor

Hai Son Nguyen (1,2)

(1) Univ Lyon, Ecole Centrale de Lyon, CNRS, INSA Lyon, Université Claude Bernard Lyon 1, CPE Lyon, CNRS, INL, UMR5270, Ecully 69130, France (2) Institut Universitaire de France (IUF), Paris, France

Non-perturbative radiation-matter coupling between dipole-active material excitations and confined modes of the electromagnetic field leads to the concept of polaritons, i.e., hybrid excitations of mixed nature involving at least two fields with different characteristics [1]. Exciton-polaritons, in particular, are mixed light-matter excitations resulting from the strong coupling regime between exciton in semiconductors and confined photons. Harnessing these hybrid excitations provides a rich playground to explore fascinating fundamental features, as out-of-equilibrium Bose-Einstein condensation and quantum fluids of light, plus novel mechanisms to be exploited in optoelectronic devices. In this talk, I will present the theory and experimental realizations of the strong coupling regime between excitons in quantum wells and a peculiar confined photon state called Bound state In a Continuum (BIC). BICs are peculiar localized states that are forbidden to radiate despite lying in a continuum of propagating waves [2]. These states were first predicted by Von Neumann and Wigner in 1929, and were once regarded as an “exotic” quantum mechanical effect. The origin of BICs is nowadays fully unraveled as a particular solution of wave equations, which has led to their exploitation in other fields where it is straightforwardly attributed to destructive interference mechanisms or symmetry mismatches. Interestingly, each photonic BIC in an optical lattice is attributed to a topological charge pinned at a polarization singularity in the momentum space [2]. This topological nature will be perfectly transferred to the polaritonic states once the strong coupling regime is established. As proofs of concept, I will show the experimental demonstration of a Bose Einstein condensation in a polariton bound state in the continuum [3]. This macroscopic states has been achieved with traditional inorganic quantum wells at cryogenic temperature. Finally, I will present the first demonstration demonstration of polariton BIC at room temperature using hybrid organic-inorganic quantum wells [4].
References :
[1] D. N. Basov et al., “Polariton panorama", Nanophotonics, 10, 549-577, 2021.
[2] C. W. Hsu et al., “Bound states in the continuum," Nature Reviews Materials, 1, 16048, 2016
[3] V. Ardizzone et al., “Polariton Bose-Einstein condensate from a bound state in the continuum," Nature, 605, 447-452, 2022.
[4] N. H. M. Dang et al., “Realization of polaritonic topological charge at room temperature using polariton bound states in the continuum from perovskite metasurface," Advanced Optical Materials, 10, 2102386, 2022.

Presenter: Nguyễn Hải Sơn