A theory of angle-resolved photoemission (ARPES) in doped charge-transfer :.1ott
insulators is developed taking into account the realistic band structure, (bi)polaron formation
due to the strong electron-phonon interaction, and a random field potential. We
derive the coherent part of the ARPES spectra with the oxygen hole spectral function calculated
in the non-crossing (ladder) approximation and with the exact spectral function
of a one-dimensional hole in a random potential. On the basis of this theory,eplanations
are proposed for several features of the ARPES spectra taken from the cuprate superconductors.
These Include the polarisation dependence and spectral shape in YBa2Cu307
and YBa2CU.jOS. The theory is compatible with the doping dependence of kinetic and
thermodynamic properties of the cuprates as well as with the d-wave symmetry of the
superconducting order parameter.
The scattering cross section of a Coulomb potential screened by a charged Bose gas
(CBG) is calculated both above and below the Bose-Einstein condensation temperature,
using the variable phase method. In contrast with the BCS superconductor, the screened
scattering potential and quasiparticle lifetime are found to be very different in the superconducting
and normal states. We apply the result to explain the appearence of a sharp
peak in the ARPES spectra in some cup rates below the superconducting transition.
The charged Bose gas model for the upper critical field in the cuprates is extended to
explain the crossing point in the curves of induced magnetization divided by the square
root of field against temperature in the less anisotropic cuprates. This model has already
been shown to provide a parameter-free expression for Te in a wide range of cuprates.
A Doctoral Thesis. Submitted in partial fulfilment of the requirements for the award of Doctor of Philosophy of Loughborough University