Resonant-energy relaxation of terahertz-driven two-dimensional electron gases

We present experimental studies of energy loss from quasi-two-dimensional electron gases that are driven to a nonequilibrium steady state by intense, ultrahigh-frequency fields. For the Alₓ{Ga}_{1{{-}}x}$As/GaAs heterostructures studied, longitudinal-optical (LO) phonon emission dominates energy loss across the previously unexplored frequency range from 0.2 to 3.5 THz, at moderate electron temperatures. We find an unexpected resonance in the absorbed power that is consistent with an increase near 0.5 THz in either the net LO phonon emission rate, or in the high-frequency mobility.