Relaxation of the cyclotron spin-flip excitation in a spin-unpolarized quantum Hall system

Abstract

Cyclotron spin-flip excitation in an even-integer quantum Hall system is the lowest-energy excitation separated from the ground state by the gap slightly smaller than the cyclotron energy, and from the upper magnetoplasma excitation by the Coulomb gap [1, 2]. At the filling factor ν = 2 in a real system these gaps are in the vicinity of 10 meV and 0.5 meV and thus are much larger than the Zeeman gap (∼ 0.1 meV) and temperature (< 0.01 meV) respectively. Under these conditions the cyclotron spin flip excitation can not relax in a purely electronic way but only with emission of a short-wave phonon (k ∼ 3 107 /cm). As a result the relaxation in a modern wide-thickness quantum well occurs very slowly, the characteristic relaxation time being ∼ 1 s. The cyclotron spin-flip excitation in the narrow vicinity of filling factors ν = 2, 4, ... should therefore be considered as a collective metastable excitation in the quantum Hall system.