Paramagnetic metal-insulator transition in the 2D Hubbard model

TL;DR

This study uses finite temperature Quantum Monte-Carlo simulations to identify a clear paramagnetic metal-insulator transition in the 2D Hubbard model at half-filling, revealing details of gap formation and spectral changes.

Contribution

First detailed finite temperature simulation showing the metal-insulator transition and spectral evolution in the 2D Hubbard model at half-filling.

Findings

Transition occurs at U_c=4t with no band narrowing in the metallic phase.

The Mott-Hubbard gap opens gradually with increasing U.

Gap formation begins at (pi,0), similar to pseudogap behavior in cuprates.

Abstract

We study the transition from paramagnetic metal to paramagnetic insulator by finite temperature Quantum Monte-Carlo simulations for the 2D Hubbard model at half-filling. Working at the moderately high temperature T=0.33*t where the spin correlation length has dropped to 1.5 lattice spacings, and scanning the interaction strength U, we observe an unambiguous metal-insulator transition with onset at U_c=4t. In the metallic phase there are no indications of any `correlation narrowing' of the band width, nor for any decrease of spectral weight at the Fermi energy. The Mott-Hubbard gap opens gradually with increasing U and is accompanied by the formation of side bands near the Fermi energy. In the first stages of gap formation the gap opens at (pi,0), reminiscent of the `pseudogap' phenomenology in cuprate superconductors.