Metal-Insulator Transition and Many-Body Band Structure of the Hubbard Model

Abstract

We study the excitation spectra of the Hubbard model by means of Quantum- Monte-Carlo simulations of finite clusters. We focus on two issues: first the metal-insulator transition in the half-filled 2D Hubbard model as a function of t/U This is done at elevated temperature T = t/3, where no more long range antiferromagnetic spin correlations remain, and on lattices up to 24 x 24. We discuss the evolution of the single-particle spectrum and the self-energy as the system goes through the transition. Second, we study the single-particle band structure at U/t = 8 and T = t/3 focussing on the interpretation of the ’band structure’ and the evolution of the Fermi surface with doping. A simple generalization of the Hubbard-I approximation reproduces the band structure at half-filling quite well, and the Fermi surface volume evloves with doping in a very similar way as predicted by the Hubbard-I approximation.