Observation of the Dissipative Parametric Gain in a GaAs/AlGaAs Superlattice

Parametric generation of oscillations and waves is a paradigm, which is known to be realized in various physical systems. Unique properties of quantum superlattices allow to investigate high-frequency phenomena induced by the Bragg reflections and negative differential velocity of the miniband electrons. Effects of parametric gain in the superlattices have been earlier discussed in a number of theoretical works, but their experimental demonstrations are so far absent. Here, we report on the first observation of the cavityless parametric generation in a subcritically doped GaAs/AlGaAs superlattice subjected to a dc bias and a microwave pump. We argue that the dissipative parametric mechanism originates from a periodic variation of the negative differential velocity. It enforces excitation of slow electrostatic waves -- the undamped drift-relaxation modes of the superlattice -- that provides a significant enhancement of the gain coefficient. This work paves the way for a development of a miniature solid-state parametric generator of GHz\nobreakdash--THz frequencies operating at room temperature.