Synchronization and Chaos Induced by Resonant Tunneling in GaAs/AlAs Superlattices.

A semiconductor superlattice represents an ideal one-dimensional nonlinear dynamical system with a large number of degrees of freedom. The effective nonlinear coupling originates from sequential resonant tunneling between adjacent wells. We have observed spontaneous chaotic and periodic current oscillations in a doped GaAs/AlAs superlattice by changing only the applied bias. When the system is driven with an incommensurate sinusoidal voltage for a fixed bias, transitions between synchronization and chaos are observed via pattern forming bifurcations. A driving signal of sufficiently large amplitude can suppress the occurrence of chaos and produce a synchronized oscillation mode with a subharmonic of the driving frequency.