Spectroscopy of Wigner crystal polarons in an atomically thin semiconductor

TL;DR

This paper reports the optical observation of Wigner crystal polarons in a monolayer WSe2, revealing new hybrid excitations that connect electronic order with optical properties and can be controlled magnetically and optically.

Contribution

It introduces the concept of Wigner crystal polarons as a new type of light-matter excitation in two-dimensional materials, linking collective electronic order with optical phenomena.

Findings

Observation of new optical resonances associated with Wigner crystal polarons

Wigner crystal polaron energies depend on lattice constant and exciton-polaron hybridization

Control of Wigner crystal spin state via magnetic and optical methods

Abstract

Strongly interacting electrons in two-dimensional systems can spontaneously break translational symmetry, forming a periodic Wigner crystal. Although these crystals have been realized in several platforms, experimental studies of their collective many-body excitations in the absence of a magnetic field remain an outstanding challenge. Here, we access this regime optically by uncovering Wigner crystal polarons: novel light-matter excitations arising from the dressing of excitons by collective excitations of the Wigner crystal. These hybrid quasiparticles manifest as new optical resonances in cryogenic reflectance spectra of a charge-tunable WSe$_2$ monolayer, appearing concurrently with previously identified exciton umklapp transitions. In contrast to the latter, the energies of Wigner crystal polarons are governed not only by the electronic lattice constant but also by their hybridization with attractive exciton-polarons, whose strength is controlled by electronic interactions. These novel many-body excitations provide an optical interface to the spin state of the Wigner crystal, which as we demonstrate, can be controlled both magnetically and optically. Our work establishes layered materials as a unique platform for exploring dynamical impurity dressing by strongly correlated electronic orders.