Kicked Hall Systems: Generic Suppression of Weak Chaos on a Universal Stochastic Web


  Moti Ben-Harush and Itzhack Dana  
Minerva Center and Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel

A novel realistic Hamiltonian model system is introduced, the "kicked Hall system". This is a charged particle in a uniform magnetic field (in the z-direction) and in a uniform electric field (in the y-direction), periodically δ-kicked in time by a cosine potential with strength K in the x-direction. The electric-field strength is measured by a dimensionless parameter β. In the absence of an electric field (β = 0) and under certain resonance conditions (i.e., precisely four kicks in one cyclotron period), it is well known that the system exhibits a global (unbounded) chaotic diffusion in the velocity plane for arbitrarily weak chaos (i.e., arbitrarily small K). This diffusion takes place on a stochastic web with square symmetry. The web structure and the diffusion rate strongly depend on the value of a conserved coordinate xc of the cyclotron orbit center.

For β ≠ 0, xc is not conserved but vary linearly in time (Hall effect). We derive, for generic rational values of β, an exact expression of the integrable effective Hamiltonian Heff for the system up to (and including) second order in K; this Hamiltonian describes in an average sense the basic phase-space structure in the weak-chaos regime. We find that, except of very special cases, the first-order term of Heff  always vanishes while the second-order term is always independent on the initial value xc(0) of xc and corresponds to a simple universal stochastic web. All this implies a generic suppression of weak chaos and chaotic diffusion on the universal web for essentially all values of β and xc(0), in sharp contrast with the β = 0 case, where the first-order term vanishes only for one value of xc.

The first-order term does not vanish only for two rational values of β and is dependent on xc(0) in these cases. This term implies that ballistic motion in velocity occurs for generic xc(0) while a stochastic web arises only for special "critical" values xcc(0) of xc(0). The ballistic-transport rate vanishes like |xc(0) - xcc(0)| as xc(0) approaches xcc(0)