Nonreciprocal coupling triggers pinning-depinning transitions of wavefronts in bistable systems chains

Coupled discrete systems with reciprocal and nonreciprocal couplings exhibit unexpected and counterintuitive phenomena compared to continuous systems. We investigate the pinning-depinning transition induced by nonreciprocal coupling in nonlinear wave propagation connecting different equilibria in bistable system chains. Theoretically, based on a prototype model of a bistable chain system with nonreciprocal coupling, we show that the latter triggers pinning-depinning transitions of fronts between homogeneous states. Experimentally, we study a chain of bistable systems with nonreciprocal coupling by employing a liquid-crystal light valve with nonreciprocal optical feedback. This system exhibits the propagation of fronts between homogeneous states. The fronts display a pinning-depinning transition by increasing the nonreciprocal coupling, achieved by increasing optical feedback offset. Close to the bifurcation, the front velocity is characterized by a square root law as a function of the bifurcation parameter. We can adequately account for the experimental observations using a tight-binding theoretical model.