This proposal is for theoretical research on the construction and solution of charge-spin models for correlated-electron systems, with application to both bulk materials (high Tc cuprates) and nanoscale structures with potential for future quantum-coherent devices.
Theoretical techniques will include a recently developed finite cluster method, degenerate per- turbation theory and quantum Monte Carlo simulations. These will be applied to the following problems. 1. Investigation of low-energy properties in the normal-state of the high Tc superconductors by approximate but accurate solutions of large clusters ( l00CuO2 'cells'). This will include the determination of correlation functions, optical conductivity and deviations from Fermi-liquid behaviour. 2. Accurate determination of effective single-band charge-spin parameters for copper-oxide planes from realistic multi-band models. This will extend earlier work and will be particularly directed towards the identification of pairing interactions.
3. Investigation of collective behaviour and critical phenomena in a quantum dot array modelled by a multi-band Hubbard Hamiltonian. 4. Detailed study of transport through a semiconducting quantum dot containing electrons at low density and in the presence of defects. This will include an investigation of persistent currents in nanoscale, two-dimensional rings.