Here we present the first time measurements in two-dimensional (2D) hole gases of the intrinsic photo-induced anomalous Hall effect (Pl-AHE) and the circular photogalvanic effect (CPGE) in perpendicular magnetic field. Both these spin-transport effects are manifested in systems with broken space-time inversion symmetry. Their underlying physics may be explained in terms of the Berry phase in momentum space or by using symmetry considerations. We have used a number of techniques to characterise the samples and to study the spin-transport: magneto-transport measurements, such as Shubnikov - de Haas and quantum Hall revealed the samples' mobility and concentration; polarised and unpolarised photoluminescence and photoluminescence excitation at zero magnetic field gave information about energy levels in the quantum wells so that the samples could be resonantly excited, and in magnetic field these latter magneto-optical measurements were directly compared to the spin-transport data. To measure the photoexcited spin-dependent voltages, samples were illuminated with circularly polarised light which created a nonequilibrium spin-polarisation. The ion was modulated using an electro-optical modulator and the resulting voltage from the samples was detected in phase with the modulation signal. This voltage was then measured as a function of magnetic field, laser helicity and laser power density, sample temperature, current through the sample, etc. This study has shown that at zero magnetic field no intrinsic photoinduced anomalous Hall effect is measurable (within the measurement error, under interband excitation), but that a photoinduced spin dependent voltage is detectable in the perpendicular magnetic field. The measured voltage starts to be pronounced above 1T. The effect has also been found to exist only in 2D hole gases grown on low symmetry crystallographic planes, such as (311).
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:501276 |
| Date | January 2009 |
| Creators | Vasyukov, Denis |
| Publisher | University of Exeter |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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