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Title: Electron-electron interactions in GaAs quantum wires
Author: Chen, T.-M.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2009
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The first experiment presents a novel method for continuously tracking the energies of the 1D subbands as a function of carrier density. I show a peculiar dc conductance feature in the region where the so-called 0.85(2e2/h) plateau in differential conductance is observed, directly demonstrating the pinning effect of the energy level of the minority spin-up electrons. A model concerning providing for non-linear population of the 1D subband with dc bias is proposed to explain the unusual differential conductance value of the 0.85(2e2/h) plateau. The second experiment shows that a fully spin-polarised current, consisting of a single spin-type only, can be created without external magnetic fields. When a source-drain bias lifts the momentum degeneracy, the dc measurements show that it is possible to achieve a unidirectional transport with a ferromagnetic order and this ordered spin array is destroyed once transport in both directions commences. The degree of spin polarisation of currents, between full spin polarisation, partial spin polarisation, and spin degeneracy, is thus simply controlled by source-drain bias and split-gate voltage, something of considerable value for spintronics. I then present four odd-even spin phenomena in the third experiment, showing clear evidence that a quasi-one-dimensional system tends to spontaneous spin polarisation with the energy band of minority spin-up electrons being reluctant to populate, thus widening the energy gap between two spin types. Variation of g-factor within a single subband is measured using a dc conductance technique, showing the g-factor oscillates as the 1D subbands are filled one by one with increasing carrier density. The last experiment introduces new experimental data of the zero-bias anomaly (ZBA), showing clear evidence that the ZBA observed in quantum wires in fact has a different origin from the Kondo effect seen in quantum dots. I propose a phenomenological model wherein the zero-bias anomaly in 1D quantum wires is in fact attributed to a upward shift of the 1D subband energy with source-drain bias.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available