Charged Excitons in the Quantum Hall Regime: Optical Probe of Fractionally Charged Quasiholes

Abstract

We review recent optical experiments on dilute two-dimensional electron systems (2DES) at very low temperatures (\(T<0.1\) K) and high magnetic fields. In photoluminescence experiments on a 2DES subjected to a quantizing magnetic field around \(\nu=1/3\), we have observed an anomalous dispersion of the charged excitons. We have found that the anomaly exists only at a very low temperature \((0.1\) K) and an intermediate electron density \((0.9 \times 10^{11}\) cm\(^{-2})\). It is explained to occur due to the perturbation of the incompressible liquid at \(\nu=1/3\). The perturbation is induced by the close proximity of a localized charged exciton which creates a fractionally-charged quasihole in the liquid. The intriguing experimentally observed puzzle that the anomaly (2 meV) can be destroyed by applying a small thermal energy of \(\sim\) 0.2\,meV is thereby resolved, as this energy is enough to close the quasihole energy gap. This work presents a first ever probe of the quasihole gap in a quantum Hall system.