Optical Detection of Integer and Fractional QHE in GaAs: Extension to the Electron Solid
Ten years on from the discovery of the integer QHE (IQHE) , and the subsequent discovery of condensation of electrons into an incompressible liquid — the fractional QHE (FQHE) , experiments are still largely restricted to electrical transport studies. Whilst there is a report of an optical measurement of the FQHE in a Si structure at 1.5K , optical experiments that probe the QHE in GaAs have remained a major challenge [4,5]. An important advance was made by the observation of anomalies in the energy of photoluminescence near v = 2/3 and v = 1 from a GaAs multiple quantum well at 0.4K . In this paper we report a definitive detection of both the integer and fractional QHE in GaAs, using intrinsic bandgap photoluminescence, by a study of integer states from v = 1 to 10 and of the v = 2/3 hierarchy out to the 5/9 daughter state, in an ultra-high mobility single heterojunction at 120mK . At higher fields the photoluminescence spectra are mapped out at 80mK through FQHE states of the v = 1/3 and 1/5 hierarchies. Of particular interest is a new photoluminescence peak that becomes clearly resolved in the region v < 1/5. The appearance of this peak at v ≃ 1/5 correlates with the rapid onset of a substantial non-linear out-of-phase conduction that has recently been shown to arise from threshold behaviour that may be associated with crystallisation [8, 9]. It also correlates in filling factor with the onset of a resonant radio-frequency absorption in this sample which maps out a phase boundary in the B-T plane .
KeywordsLaser Illumination Luminescence Line Quasiparticle Energy Density Depletion Integer Quantum Hall Effect
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