Abstract
By direct absorption spectroscopy and comparison to photoluminescence (PL), we investigate negatively charged excitons in dilute two-dimensional electron systems at temperatures down to in the regime of the fractional quantum Hall effect. At very low temperatures, for filling factor an additional excitation appears in the PL spectrum, between the well-known singlet and triplet excitons. The observation of a similar excitation by PL was reported very recently [G. Yusa et al., Phys. Rev. Lett. 87, 216402 (2001)], and the excitation was assigned, in spite of the PL intensity similar to that of the neutral exciton, to be due to a dark triplet exciton. By comparing PL and direct absorption spectra in optically thin samples at we can identify the new excitation indeed as a “dark” mode, since we find that the oscillator strength is much smaller than those of the “bright” modes.
- Received 27 September 2001
DOI:https://doi.org/10.1103/PhysRevB.65.081301
©2002 American Physical Society