Tunable Terahertz Cyclotron Emission from Two-Dimensional Dirac Fermions

We report on the emission of Terahertz radiation from Landau quantized Dirac electrons in HgTe/CdHgTe based quantum wells. We show that this cyclotron emission is continuously tunable with magnetic field from 500 GHz up to 2.5 THz. Moreover, given the relativistic nature of charge carriers, the cyclotron mass and therefore the emitted frequency are also tunable with the electron density. These results pave the way for the long-awaited Landau laser which could additionally be tunable by a gate voltage with a fixed magnetic field.