Explosive Bifurcation to Chaos in Weakly Coupled Semiconductor Superlattices

The bifurcation scenario to chaos has been studied for vertical transport in an incommensurately driven superlattice system. With increasing driving amplitude, quasiperiodic, frequency-locked, and chaotic oscillations are identified by using Poincar\'e maps, which show a variety of attractors in the chaotic regime. The dimension of the attractor is abruptly increased in the transition process, i.e., the bifurcation between frequency locking and chaos is explosive. However, the bifurcation pattern depends strongly on the applied dc bias, providing clear evidence that the system is spatially inhomogeneous in the vertical direction.