Hamiltonian Flow Equations and the Electron-Phonon-Problem

In this thesis we investigate the electron-phonon-system using the method of Flow Equations for Hamiltonians. In this continuous diagonalisation process the one particle energies and interaction constants are subject to a series of transformations, the ``flow'' of the Hamiltonian. They depend on a flow parameter l varying from zero to infinity. We give a proof that the asymptotic behaviour of the flow of the one-particle energies for large l is given by a constnat over squareroot of l behaviour. The constant may contain terms logarithmic in l and depends on electronic momentum k. This result is used to show that the transformation does lead to a blockdiagonal Hamiltonian decoupling the electron and the phonon subsystems. We obtain the same renormalization of the phonon energies as Wegner and Lenz, who neglected the shift of the electronic one-particle energies. The dependency of the renormalization of the electronic energies on the distance to the fermi surface is calculated. We investigate the transformation of the electronic one-particle operators. In the appendix we present a rigorous proof of the asymptotic behaviour. The l-dependency is changed by including an additional logarithmic factor and this refined asymptotic behaviour is investigated.

Level thesis:degree_level

thesis.doctoral

Grantor dc:publisher

Universität Heidelberg

Year

2002

Author dc:creator

• Schütte, Albrecht

Contributors dc:contributor

• Wegner, Franz

Repository record source_url

http://www.ub.uni-heidelberg.de/archiv/2105

OAI identifier oai:identifier

oai:archiv.ub.uni-heidelberg.de:2105