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Title: Anomalous correlations in low dimensional metals
Author: Dias, R. A. G.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1996
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Dimensionality is a determinant factor in the behaviour of interacting electron systems. The cuprates and the organic superconductors are examples of systems of reduced dimensionality with anomalous normal state correlations. This thesis presents a study of one and two-particle correlations, namely, the single particle spectral function and the pair propagator, for electron systems with low dimensionality. The single particle spectral function is probed by angle resolved photoemission experiments. Theories of photoemission are presented. One dimensional metals belong to the Luttinger liquid universality class, sharing the low energy properties of the Luttinger Model. A study of the spectral and Green's functions of this model is given. The spectral functions reflect the Fermi liquid breakdown due to the anomalous correlations and spin-charge separation which are typical of this model. The upper critical field Hc2 of a type-II superconductor is a probe of anomalous normal state pair correlations. We study the weak coupling superconducting instability equation for a simple quasi-one dimensional system, the two-dimensional highly anisotropic tight-binding model for each typical filling. The magnetic field in conjunction with the underlying lattice induces a dimensional crossover which leads to divergent mean field Hc2 curves in the strong anisotropy limit. We study the suppression of the mean field superconducting instability of a clean weak coupling BCS superconductor in a finite magnetic field at a 2D van-Hove singularity. The absence of a velocity scale is shown to lead a spectacular deviation from the Fermi liquid BCS result, such as upward curvature and a strong enhancement of the upper critical field relative to Tc, Hc2(0) ˜ Tc√2 in contrast with the conventional BCS scaling Hc2(0) ˜ Tc2. The consequences for the superconducting transition of a Luttinger liquid-like spin-charge separated normal state are explored. We show that spin-charge separation leads to an enhancement of the superconducting critical temperature compared with the conventional BCS result. The spatial decay of the pair propagator is shown to contain a logarithmic correction relative to the free Fermi gas result in a finite interval between the spin and charge thermal lengths which leads to deviations from the usual BCS parabolic-like Hc2 behaviour.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available