Beyond the ordinary acoustoelectric effect: Superluminal phenomena in the acoustic realm and phonon-mediated Bloch gain

It has been shown that coherent phonons can be used as a potent tool for controlling and enhancing optoelectronic transport properties of nanostructured materials. Recent studies revealed interaction acoustic fast-moving carriers in semiconductor heterostructures accompanied by electron-phonon instabilities cause ordinary induced Cherenkov effects. However, the development such is still poorly understood. Our study shows other supersonic phenomena, beyond instability, are possible nonequilibrium charge miniband superlattices (SLs) driven an plane wave. Using semiclassical nonperturbative methods elements bifurcation theory, we find conditions onset dynamical (bifurcations) which caused emission specific SL electrons, their back action on electrons. Notably, underlying radiation mechanism connected either to normal or anomalous Doppler effects full accordance with Ginzburg-Frank-Tamm theory. The appearance also discussed relation formation electron bunches propagating through spatially periodic structure SL. When amplitude wave exceeds certain threshold, developed system manifested drift velocity reversals, resonances sound attenuation, absolute negative mobility. We demonstrate discovered superluminal phenomena utilized tunable broadband amplification generation GHz-THz electromagnetic waves, creates ground novel phononic devices.