Nonlinear Terahertz Electroluminescence from Dirac-Landau Polaritons

We report Dirac-Landau polaritons observed by terahertz (THz) magnetoreflectivity spectroscopy, demonstrating strong coupling between cyclotron transitions of two-dimensional Dirac fermions in HgTe quantum wells and optical cavity modes. Under pulsed electrical injection we observe efficient nonlinear electroluminescence, with a strongly out-of-equilibrium polariton distribution dominated by emission from the upper polariton branches. Model analysis of the bias-dependent emission intensity and spectral narrowing indicates a polariton occupancy per mode approaching unity, with a possible contribution from stimulated polariton emission in the spectral region of the upper anticrossing. These results open prospects toward Dirac-Landau polariton condensates and low-threshold, tunable THz polariton lasers based on cyclotron emission.