Systematic 1/S study of the 2D Hubbard model at half-filling

TL;DR

This paper systematically studies the 2D Hubbard model at half-filling using a 1/S expansion, revealing magnetic and spectral properties consistent with large S limits and providing insights into fermionic spectrum corrections.

Contribution

It introduces a systematic 1/S expansion approach for the 2D Hubbard model, extending previous large S calculations to include fermionic spectrum corrections.

Findings

Magnetic susceptibility aligns with large S Heisenberg antiferromagnet results

Fermionic spectrum corrections lift degeneracy along magnetic Brillouin zone edge

Minima in spectra occur at (+- pi/2, +- pi/2)

Abstract

The 2D Hubbard model is extended by placing 2S orbitals at each lattice site and studied in a systematic 1/S expansion. The 1/S results for the magnetic susceptibility and the spectra of spin-wave excitations at half-filling are consistent with the large S calculations for the Heisenberg antiferromagnet. The 1/S corrections to the fermionic spectrum lift the degeneracy along the edge of the magnetic Brillouin zone yielding minima at (+- pi/2, +- pi/2). Relation to previous papers on the subject is discussed.