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Kicked Hall Systems: Generic Super-Weak Chaos on a Universal Stochastic Web
Moti Ben-Harush , Itzhack Dana
Minerva Center and Department of Physics, Bar-Ilan University, Ramat-Gan 52900, Israel
A new realistic Hamiltonian 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, as assumed in this work), 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. In particular, for K << 1 and for very special values of xc, the web thickness and the diffusion rate are much smaller than those for generic xc. This phenomenon was first discovered as a classical fingerprint of quantum antiresonance in the β=0 system. We shall refer to this rare phenomenon for β=0 as "super-weak chaos''.
For β≠0, xc is not conserved but varies linearly in time (Hall effect). We derive, for generic rational values of β/(2π), an exact expression of the effective integrable 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 essentially just two rational values of β/(2π), the first-order term of Heff always vanishes while the second-order term is always independent of the initial value xc(0) of xc, leading to a stochastic web with a simple "universal" web skeleton. This precisely implies super-weak chaos on the universal web skeleton in a much more generic fashion that in the β=0 case.
For the two exceptional rational values of β/(2π), the leading-order term of Heff is either linear or quadratic in K and depends on xc(0). We show that this term implies in both cases ballistic motion in velocity for generic xc(0), with a stochastic web arising 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).