Competing hyperfine and spin-orbit couplings: Spin relaxation in a quantum Hall ferromagnet

摘要

Spin relaxation in a quantum Hall ferromagnet, where filling is v = 1,1/3,1/5,..., can be considered in terms of spin-wave annihilation/creation processes. Hyperfine coupling with the nuclei of the GaAs matrix provides spin nonconservation in the two-dimensional electron gas and determines spin relaxation in the quantum Hall system. This mechanism competes with spin-orbit coupling channels of spin-wave decay and can even dominate in a low-temperature regime where T is much smaller than the Zeeman gap. In this case the spin-wave relaxation process occurs nonexponentially with time and does not depend on the temperature. The competition of different relaxation channels results in crossovers in the dominant mechanism, leading to nonmonotonic behavior of the characteristic relaxation time with the magnetic field. We predict that the relaxation times should reach maxima at B≌ 18 T in the v = 1 quantum Hall system and at B ≌ 12 T for that of v ≈ 1/3. We estimate these times as ～10-30 μs and ～2-5 μs, respectively.