SPIN-FLIP EXCITATIONS IN THE FRACTIONAL-QUANTUM-HALL-EFFECT REGIME STUDIED BY POLARIZED PHOTOLUMINESCENCE OF CHARGED EXCITONS

We report on a tow-temperature magneto-optical study of the spin-singl et charged exciton (X-s(-)) transitions in GaAs/Al0.1Ga0.9As modulatio n-doped multiple quantum wells with an optically tuned two-dimensional electron gas (2DEG) density corresponding to a filling factor in the range 0 < nu less than or equal to 1. We find strong evidence for the effect of 2DEG magnetic correlations on the X-s(-) spin-resolved trans itions. The energy difference between the sigma(-)- and sigma(+)-polar ized X-s(-) photoluminescence (PL) intensity maxima is found to oscill ate with varying nu. The numerical derivative of these oscillations wi th respect to nu shows minima at odd denominator rational fractions an d maxima at even denominator fractions, similar to the longitudinal re sistivity measured in the fractional quantum Hall effect. At nu = 1, t he observed sigma(-)-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(-).