Robin Nicholas

Abstract:

Measurements of the fractional quantum Hall effect energy gaps at high pressures are presented that provide evidence for the existence of composite Skyrmions. Just as charged spin textures known as Skyrmions are thought to be the lowest lying excitations for electrons at v = 1, we show that composite Skyrmions can be formed at v = 1/3 when the electron g-factor is sufficiently small. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We report the measurement of magnetophotoluminescence spectra in high-mobility GaAs/GaAlAs heterojunctions as a function of density and temperature. For densities below 1 x 10(11) cm(-2) the PL is excitonic in nature, but at higher densities a transition occurs at Landau occupancies below v = 1 to a "free-hole" luminescence, accompanied by a red shift of the FL. The transition is strongly temperature dependent. We also describe the observation of a FIR modulation of the PL signal, which is found to modulate only the excitonic PL. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We report measurements of photo-luminescence from GaAs/AlGaAs heterojunctions in the ultra-quantum limit. New features are observed for low electron densities at high magnetic field, which we suggest are associated with the formation of negatively charged excitons, both singlet and triplet states. The dependence of the spectra on temperature and carrier density are presented in support of this theory. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

A 60 T non-destructive pulsed magnet is developed for use with the continuously tuneable free electron laser "FELIX". Far infrared cyclotron resonance experiments were performed using the energy range of FELIX (5-100 mu m) to study the effect of strong confinement on the charge carriers in delta-doped InSb. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We describe the properties of the strongly interacting 2-D electron gas in high magnetic fields whose properties can be described in terms of the formation of composite fermions at fractional Landau level occupancy. For a Landau level occupancy v = 1 the excitations correspond to spin waves for high g-factors and magnetic fields, but when the g-factor is reduced close to zero by the use of hydrostatic pressure, there is strong evidence for the formation of Skyrmions. Studies of the composite fermions in the limit of vanishing Zeeman energy also suggest that skyrmionic excitations can occur for composite fermions. (C) 1998 Elsevier Science B.V. All rights reserved.