Wigner polarons reveal Wigner crystal dynamics in a monolayer semiconductor

Abstract: Wigner crystals, lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven quantum phase transitions. Despite decades of research, the internal dynamics of Wigner crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero-field Wigner crystals and then demonstrate that exciton spectroscopy provides a direct means to probe both static and dynamic properties of these electron lattices. We uncover striking optical resonances that we identify as Wigner polarons, quasiparticles formed when the electron lattice is locally distorted by exciton-Wigner crystal coupling. We further achieve all-optical control of spins in the Wigner crystal, directly probing valley-dependent Wigner polaron scattering well above the magnetic ordering temperature and in the absence of any external magnetic field. Finally, we demonstrate optical melting of the Wigner crystal and observe intriguingly different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results open up exciting new avenues for elucidating electron dynamics and achieving ultrafast optical control of interaction-driven quantum phase transitions in strongly correlated electron systems.