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Title: The Shubnikov-de Haas effect in graphite intercalcates
Author: Bender, A. S.
Awarding Body: University of London
Current Institution: Imperial College London
Date of Award: 1973
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The Fermi surface of pristine graphite is discussed in relation to current models of the energy band scheme paying particular attention to the origin of the band parameters and to the influence of the trigonal warping parameter, γ3, on the surface geometry. This provides a basis for the study of the oscillatory magnetoresistance in pyrolytic and single crystal graphites. A time-independent Green's function approach to this problem is reviewed in detail, having the advantage over the Lifshitz-Kosevich treatment that state lifetimes, and thus Dingle temperatures, are an integral part of the analysis. Brief attention is also given to the time-dependent Green's function approach as it relates to collision broadening. The Shubnikov-de Haas effect has been investigated in graphite and, for the first time, in dilute graphitebromine compounds up to approximately the C₁₄₀Br stage of intercalation. It is concluded that bromine intercalation of single crystal and well oriented pyrolytic graphite leads to the formation of several distinct, coexisting phases within the sample. These are best considered as graphitic regions of characteristic Fermi energy and c-axis dimension, separated by condensed monolayers of Br ions which have accepted their ionic charge from the n electron system of the graphite matrix. Such intercalated bromine acceptors allow observation of SdH oscillations of the hole carriers which are dominant in each phase since, being located in interplanar spaces, they do not greatly increase the collision broadening of the Landau levels existing in the graphitic regions. Wide variations are observed in the relative contributions of electrons and holes to the oscillatory magnetoresistance of pristine graphites of different origin. From comparison with neutron irradiated samples which contain negatively charged point defects, it is argued that charge-selective scattering accounts for these variations. Selective scattering is then linked with the trigonal fluting of the graphite Fermi surfaces to interpret preliminary measurements of Dingle temperatures made as a function of the angle 0 between the magnetic field and sample c-axis.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available