Collinear antiferromagnetic state in a two-dimensional Hubbard model at half filling

TL;DR

This paper investigates the phase transitions and electronic properties of a half-filled Hubbard model on a square lattice, revealing a metal-insulator transition within the collinear antiferromagnetic state influenced by on-site repulsion.

Contribution

It demonstrates the existence of a metal-insulator transition in the CAF state and maps the phase diagram, including first- and second-order transitions, in a two-dimensional Hubbard model.

Findings

CAF state is metallic at low repulsion with van Hove singularity effects.

CAF state becomes a Mott insulator at high repulsion.

Phase diagram includes first-order CAF-antiferromagnetic and second-order CAF-paramagnetic transitions.

Abstract

In a half-filled Hubbard model on a square lattice, the next-nearest-neighbor hopping causes spin frustration, and the collinear antiferromagnetic (CAF) state appears as the ground state with suitable parameters. We find that there is a metal-insulator transition in the CAF state at a critical on-site repulsion. When the repulsion is small, the CAF state is metallic, and a van Hove singularity can be close to the Fermi surface, resulting in either a kink or a discontinuity in the magnetic moment. When the on-site repulsion is large, the CAF state is a Mott insulator. A first-order transition from the CAF phase to the antiferromagnetic phase and a second-order phase transition from the CAF phase to the paramagnetic phase are obtained in the phase diagram at zero temperature.