Experimental observation of topological Z2 exciton-polaritons in transition metal dichalcogenide monolayers

Abstract

The rise of quantum science and technologies motivates photonics research to seek new platforms with strong light-matter interactions to facilitate quantum behaviors at moderate light intensities. Topological polaritons (TPs) offer an ideal platform in this context, with unique properties stemming from resilient topological states of light strongly coupled with matter. Here we explore polaritonic metasurfaces based on 2D transition metal dichalcogenides (TMDs) as a promising platform for topological polaritonics. We show that the strong coupling between topological photonic modes of the metasurface and excitons in TMDs yields a topological polaritonic Z2 phase. We experimentally confirm the emergence of one-way spin-polarized edge TPs in metasurfaces integrating MoSe2 and WSe2. Combined with the valley polarization in TMD monolayers, the proposed system enables an approach to engage the photonic angular momentum and valley and spin of excitons, offering a promising platform for photonic/solid-state interfaces for valleytronics and spintronics.

Polaritonic Chern insulators in monolayer semiconductors

“…These quasiparticles combine the properties of their parental photon and matter components and, thereby, provide an ideal platform to study quantum many-body physics, including Bose-Einstein condensates 1 , superfluidity 2 , and Berezinskii-Kosterlitz-Thouless transition 3 . Motivated by the recent rapid progress in topological band theory [4][5][6] , there has been of great interest in applying it to polaritonic systems and exploring novel topological phenomena intrinsic to exciton-polaritons [7][8][9][10][11][12][13] . For example, in contrast to photons that rarely interact with each other, exciton-polaritons exhibit strong nonlinearities through exciton-exciton interactions [14][15][16] , allowing for the study of nonlinear and interacting topological phenomena 6 .…”

Topological phonon-polariton funneling in midinfrared metasurfaces

“…This opens new realms for topological multiphysics, where topological phases can be transferred from one type of physical domain to another or emerge as the result of multiphysics interactions ( 14 – 16 ). Recent work has shown that interactions of light with excitons may lead to the formation of topological exciton-polaritons ( 17 – 20 ).…”

“…The addition of the hBN layer on top of the metasurface leads to coupling between photonic and phononic modes, giving rise to the formation of hybrid polaritonic states. The condition of strong coupling, required for the observation of topological phonon-polaritons ( 20 ), can be achieved when the hBN thickness exceeds ~5 nm. From this point forward, we consider the case of the 15-nm-thick hBN.…”

“…An important consequence of the strong coupling is the transfer of topological invariant from the photonic mode to the upper polaritonic mode ( 20 ), which is ultimately responsible for the formation of topologically robust helical edge phonon-polaritons. A calculation of the topological invariants shows that, for the case of a TO phonon crossing the lower photonic (EM) bulk mode [ω TO < ω EM ( k = 0)], the upper polariton acquires spin-Chern numbers C s = ±1 for the two pseudospins (supplementary note 3) ( 27 )—a scenario realized in the experiment described below.…”

Microscopic analysis of the spin-momentum locking on a Geometric Phase Metasurface

“…Considering the crucial role played by spin-momentum locking in integrated quantum optical systems [2], our elucidation of the mechanism and its relation to the near-field will undoubtedly renew the vision of the corresponding scattering process. This is important in the current applicative perspectives discussed currently in the context of optovalleytronic systems [39], non-linear hybrid metasurfaces [40], and topology-based high-resolution sensors [41].…”