Devil's staircase, spontaneous-DC bias, and chaos via quasiperiodic plasma oscillations in semiconductor superlattices

We study a plasma instability in semiconductor superlattices irradiated by a monochromatic, pure AC electric field. The instability leads to sustained oscillations at a frequency \omega 2 that is either incommensurate to the drive, or frequency-locked to it, \omega 2 = (p/q) \omega. A spontaneously generated DC bias is found when either p or q in the locking ratio are even integers. Frequency locked regions form Arnol'd tongues in parameter space and the ratio \omega 2 / \omega\ exhibits a Devil's staircase. A transition to chaotic motion is observed as resonances overlap.