Frohlich-bipolaronen in twee en drie dimensies

In this thesis, the Frohlich bipolaron is studied. As such, this work is part of the research done at the Institute for Theoretical Solid State Physics (University of Antwerp (RUCA & UIA), Antwerpen) in the fields of polaron and semiconductor physics, as initiated by prof. dr. J. T. Devreese.; The stability region for bipolaron formation is an important input parameter for the bipolaron theories of high-{dollar}Tsb{lcub}c{rcub}{dollar} superconductivity. In these theories, bipolaron formation is considered to be the relevant pair-forming mechanism and bipolarons are the analog of Cooper pairs in the BCS-theory of convential superconductors. This thesis considers the Frohlich electron-phonon interaction. Consequently, large or Frohlich-bipolarons are studied.; By means of a Feynman path-integral treatment, a detailed analytical and numerical study of the Frohlich bipolaron is presented. The Feynman (single) polaron can be obtained as a limit of the proposed model. As such, a consistent description is given of the "bipolaron {dollar}to{dollar} single polaron" transition. Furthermore, a scaling relation is derived, which makes it possible to obtain the energy and the mass of the two-dimensional bipolaron from the three-dimensional results. The fase diagram for bipolaron formation is calculated and it is shown that the stability region in two dimensions is much larger than in three dimensions.; The possible existence of two-dimensional Frohlich-bipolarons in the high-{dollar}Tsb{lcub}c{rcub}{dollar} superconductors, based on La{dollar}sb2{dollar}CuO{dollar}sb4,{dollar} is discussed on the basis of the large, anisotropic static dielectric constant in this compound.