Magnetic-field-induced suppression of electronic conduction in a superlattice

Bifurcations and chaos in semiconductor superlattices with a tilted magnetic field

We study the effects of dissipation on electron transport in a semiconductor superlattice with an applied bias voltage and a magnetic field that is tilted relative to the superlattice axis. In previous work, we showed that, although the applied fields are stationary, they act like a terahertz plane wave, which strongly couples the Bloch and cyclotron motion of electrons within the lowest miniband. As a consequence, the electrons exhibit a unique type of Hamiltonian chaos, which creates an intricate mesh of conduction channels (a stochastic web) in phase space, leading to a large resonant increase in the current flow at critical values of the applied voltage. This phase-space patterning provides a sensitive mechanism for controlling electrical resistance. In this paper, we investigate the effects of dissipation on the electron dynamics by modifying the semiclassical equations of motion to include a linear damping term. We demonstrate that, even in the presence of dissipation, deterministic chaos plays an important role in the electron transport process. We identify mechanisms for the onset of chaos and explore the associated sequence of bifurcations in the electron trajectories. When the Bloch and cyclotron frequencies are commensurate, complex multistability phenomena occur in the system. In particular, for fixed values of the control parameters several distinct stable regimes can coexist, each corresponding to different initial conditions. We show that this multistability has clear, experimentally observable, signatures in the electron transport characteristics.

Novel regimes of electron dynamics in superlattices

A superlattice (SL) is an artificial crystal in which alternating nanometre-thick layers of two or more different semiconductor materials provide a periodic potential for conduction electrons. Strong magnetic and electric fields applied to this type of structure provide a means of exploring novel regimes of electron dynamics. The applied fields lower the dimensionality of the electronic states and lead to qualitative changes in the electronic conduction. This discovery is of fundamental interest and highly relevant to the properties of other low-dimensional conductors, such as nanowires and quantum dot SLs, which are presently attracting the attention of the physics and device communities. In addition, a rare type of chaotic electron dynamics, called non-Kolmogorov-Arnold-Moser (KAM) chaotic motion, which has been theoretically studied for several decades, is observed experimentally in SLs. The onset of chaos at discrete values of the applied electric and magnetic fields is observed as a large increase in the current flow due to the creation of unbound electron orbits, which propagate through intricate web patterns in phase space. Therefore, non-KAM chaos could provide a new mechanism for controlling the electrical conductivity of the electronic devices with extreme sensitivity.