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Title: Rashba spin-splitting and terahertz quantum Hall effect for heavy holes in strained germanium quantum wells
Author: Failla, Michele
ISNI:       0000 0004 6496 4968
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2017
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Terahertz time-domain spectroscopy (THz-TDS) allows the investigation, in a noncontact fashion and in the meV range (1 THz = 4.14 meV), of the coherent motion of particles close to their equilibrium position. In contrast with other optical spectroscopy techniques, THz-TDS gives the chance to perform phase-resolved measurements and to investigate quantum coherent phenomena within different materials or systems such as two dimensional hole or electron gases (2DHGs, 2DEGs). This thesis presents a thorough characterisation - by means of THz-TD magneto-spectroscopy (THz-TDMS) and polarisation resolved (PR)-THz-TDMS – of high mobility 2DHGs in 0.8% and 1.3% compressively strained germanium quantum wells (sGe-QWs) grown on SiGe virtual substrates. These are attractive systems for electronic and spintronic devices due to the compatibility of Ge with CMOS technology as well as their finite spin-orbit interaction (SOI). The SOI, driven by structural inversion asymmetry (SIA) in modulation doped SiGe heterostructures, can lift the spin degeneracy and provide spin-split states separated by the Rashba energy Δ even at zero external magnetic field. Results presented in the following thesis proved the strain-dependence of the Rashba spin-splitting as well as a non-contact determination of the g-factor, effective mass, transport lifetime and mobility. In addition to THz-TDMS, PR-measurements determined the off-diagonal conductivity σxy(ω,B). This was obtained by analysing the Faraday effect, which was seen as a change in the polarisation of the incident THz-pulse due to the presence of carriers within the QWs, under the application of a magnetic field. Determining σxy revealed, for the first time in a 2DHG, features of the optical quantum Hall effect (OQHE), i.e. the QHE driven by an a electric field (ac THz-field). The thesis ends with introducing rotatable polarisation THz-TDS experiments to study anisotropic materials. As an outlook of the presented work, this experimental technique can be exploited in order to evaluate the anisotropic mobility in sGeQWs.
Supervisor: Not available Sponsor: Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QC Physics