12 research outputs found
Observation of exchange Coulomb interactions in the quantum Hall state at nu=3
Coulomb exchange interactions of electrons in the nu=3 quantum Hall state are
determined from two inter-Landau level spin-flip excitations measured by
resonant inelastic light scattering. The two coupled collective excitations are
linked to inter-Landau level spin-flip transitions arising from the N=0 and N=1
Landau levels. The strong repulsion between the two spin-flip modes in the
long-wave limit is clearly manifested in spectra displaying Coulomb exchange
contributions that are comparable to the exchange energy for the quantum Hall
state at nu=1. Theoretical calculations within the Hartree-Fock approximation
are in a good agreement with measured energies of spin-flip collective
excitations.Comment: 5 pages, 3 figures, to appear in PRB Rapid Communication
Suppression of nuclear spin diffusion at a GaAs/AlGaAs interface measured with a single quantum dot nano-probe
Nuclear spin polarization dynamics are measured in optically pumped
individual GaAs/AlGaAs interface quantum dots by detecting the time-dependence
of the Overhauser shift in photoluminescence (PL) spectra. Long nuclear
polarization decay times of ~ 1 minute have been found indicating inefficient
nuclear spin diffusion from the GaAs dot into the surrounding AlGaAs matrix in
externally applied magnetic field. A spin diffusion coefficient two orders
lower than that previously found in bulk GaAs is deduced.Comment: 5 pages, 3 figures, submitted to Phys Rev
Goldstone Mode Relaxation in a Quantum Hall Ferromagnet due to Hyperfine Interaction with Nuclei
Spin relaxation in quantum Hall ferromagnet regimes is studied. As the
initial non-equilibrium state, a coherent deviation of the spin system from the
direction is considered and the breakdown of this Goldstone-mode
state due to hyperfine coupling to nuclei is analyzed. The relaxation occurring
non-exponentially with time is studied in terms of annihilation processes in
the "Goldstone condensate" formed by "zero spin excitons". The relaxation rate
is calculated analytically even if the initial deviation is not small. This
relaxation channel competes with the relaxation mechanisms due to spin-orbit
coupling, and at strong magnetic fields it becomes dominating.Comment: 8 page