Nonlinear Terahertz electroluminescence from Dirac-Landau polaritons

Abstract: We report the observation of Dirac-Landau polaritons via THz magnetoreflectivity spectroscopy, demonstrating strong coupling between cyclotron transitions of two-dimensional Dirac fermions in HgTe quantum wells and optical cavity modes. We demonstrate efficient nonlinear electroluminescence, characterized by a strongly out-of-equilibrium polariton distribution dominated by emission from the upper polariton branches. Model calculations, based on the nonlinear dependence of the emission intensity and spectral narrowing with bias voltage, indicate a polariton occupancy per mode close to unity, with a significant contribution from stimulated polariton emission. These findings open promising prospects for the development of Dirac-Landau polariton condensates and low-threshold, tunable terahertz polariton lasers based on cyclotron emission.