Optical signatures of charge order in a Mott-Wigner state

TL;DR

This paper reveals how charge order in a Mott-Wigner state creates distinct optical signatures in exciton-polaron spectra, enabling optical detection of electronic correlations and spatial order in two-dimensional semiconductors.

Contribution

It demonstrates that electronic charge order modifies exciton-electron interactions, producing new optical resonances that serve as signatures of strongly correlated states.

Findings

Charge order breaks excitonic translational invariance.

New optical resonances appear due to spatially modulated interactions.

Optical spectroscopy can detect Wigner crystals and density waves.

Abstract

The elementary optical excitations in two dimensional semiconductors hosting itinerant electrons are attractive and repulsive polarons -- excitons that are dynamically screened by electrons. Exciton-polarons have hitherto been studied in translationally invariant degenerate Fermi systems. Here, we show that electronic charge order breaks the excitonic translational invariance and leads to a direct optical signature in the exciton-polaron spectrum. Specifically, we demonstrate that new optical resonances appear due to spatially modulated interaction between excitons and electrons in an incompressible Mott state. Our observations demonstrate that resonant optical spectroscopy provides an invaluable tool for studying strongly correlated states, such as Wigner crystals and density waves, where exciton-electron interactions are modified by the emergence of new electronic charge or spin order.