Dynamic nonreciprocity in loss-compensated piezophononic media

Violating time-reversal symmetry enables one to engineer nonreciprocal structures for isolating and rectifying sound and mechanical vibrations. Rectifying sound is commonly achieved in nonlinear media, but the operation is inherently linked to weak and distorted signals. Here, we show how a pronounced electron-phonon coupling in linear piezophononic media under electrical bias can generate full mechanical rectification of broad spectral width, which permits the isolation of pulsed vibrations while keeping the wave-front shape fully intact. In this context, we deliberately show how the acoustoelectric effect can provide active loss compensation against lattice anharmonicity and thermoelastic damping. Further, our predictions confirm tunable nonreciprocity at an ultralarge contrast ratio, which should open the doors for future mechanical diodes and compact ultrasonic transducers for sensing and imaging.J. C. acknowledges the support from the European Research Council (ERC) through the Starting Grant No. 714577 PHONOMETA and from the MINECO through a Ramon y Cajal grant (Grant No. RYC-2015-17156)