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It has been shown that coherent phonons can be used as a potent tool forcontrolling and enhancing optoelectronic and transport properties ofnanostructured materials. Recent studies revealed that interaction of acousticphonons and fast-moving carriers in semiconductor heterostructures can beaccompanied by electron-phonon instabilities that cause ordinary and inducedCherenkov effects. However, the development of such instabilities is stillpoorly understood. Our study shows that other supersonic phenomena, beyond theCherenkov instability, are possible for non-equilibrium charge transport in theminiband semiconductor superlattices (SLs) driven by an acoustic plane wave.Using semiclassical nonperturbative methods and elements of the bifurcationtheory, we find the conditions for the onset of dynamical instabilities(bifurcations) which are caused by the emission of specific SL phonons bysupersonic electrons, and their back action on the electrons. Notably, theunderlying radiation mechanism is connected either to normal or anomalousDoppler effects in full accordance with the Ginzburg-Frank-Tamm theory. Theappearance of induced Doppler effects is also discussed in relation to theformation of electron bunches propagating through the spatially periodicstructure of the SL. When the amplitude of the acoustic wave exceeds certainthreshold, the dynamical instabilities developed in the system are manifestedas drift velocity reversals, resonances in sound attenuation and absolutenegative mobility. We demonstrate that the discovered superluminal Dopplerphenomena can be utilized for tunable broadband amplification and generation ofGHz-THz electromagnetic waves, which creates a ground for development of novelphononic devices.

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