Magneto-transport controlled by Landau polariton states

Hybrid excitations, called polaritons, emerge in systems with strong light-matter coupling. Usually, they dominate the linear and nonlinear optical properties with applications in quantum optics. Here, we show the crucial role of the electronic component of polaritons in the magneto-transport of a cavity-embedded two-dimensional electron gas in the ultrastrong coupling regime. We show that the linear direct-current resistivity is substantially modified by the coupling to the cavity even without external irradiation. Our observations confirm recent predictions of vacuum-induced modification of the resistivity. Furthermore, photoassisted transport in the presence of a weak irradiation field at sub-terahertz frequencies highlights the different roles of localized and delocalized states.