Spin-flip excitations in the fractional-quantum-Hall-effect regime studied by polarized photoluminescence of charged excitons

Abstract

We report on a low-temperature magneto-optical study of the spin-singlet charged exciton ${(X}_{s}^{\ensuremath{-}})$ transitions in ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_{0.1}{\mathrm{Ga}}_{0.9}\mathrm{As}$ modulation-doped multiple quantum wells with an optically tuned two-dimensional electron gas (2DEG) density corresponding to a filling factor in the range $0l\ensuremath{\nu}l~1.$ We find strong evidence for the effect of 2DEG magnetic correlations on the ${X}_{s}^{\ensuremath{-}}$ spin-resolved transitions. The energy difference between the ${\ensuremath{\sigma}}^{\ensuremath{-}}$- and ${\ensuremath{\sigma}}^{+}$-polarized ${X}_{s}^{\ensuremath{-}}$ photoluminescence (PL) intensity maxima is found to oscillate with varying \ensuremath{\nu}. The numerical derivative of these oscillations with respect to \ensuremath{\nu} shows minima at odd denominator rational fractions and maxima at even denominator fractions, similar to the longitudinal resistivity measured in the fractional quantum Hall effect. At $\ensuremath{\nu}=1,$ the observed ${\ensuremath{\sigma}}^{\ensuremath{-}}$-polarized low-energy PL tail is interpreted (by a line-shape analysis) to be due to a finite-k 2DEG spin-wave emission coupled to the optical recombination of the ${X}_{s}^{\ensuremath{-}}.$