Large-$U$ limit of a Hubbard model in a magnetic field: chiral spin interactions and paramagnetism

TL;DR

This paper studies the large-U limit of a half-filled Hubbard model on a non-bipartite lattice, showing how magnetic fields induce chiral interactions that dominate low-temperature magnetic responses.

Contribution

It demonstrates that in the large-U limit, magnetic fields induce chiral interactions that can surpass Pauli spin coupling effects, with explicit models showing finite chiral susceptibility.

Findings

Chiral interactions are induced at order 1/U^2 in a large-U Hubbard model.

The ground state is a singlet with a gap, leading to zero spin susceptibility.

Chiral susceptibility remains finite and paramagnetic at low temperatures.

Abstract

We consider the large-$U$ limit of the one-band Hubbard model at half-filling on a non-bipartite two-dimensional lattice. An external magnetic field can induce a three-spin chiral interaction at order $1 / U^2 ~$. We discuss situations in which, at low temperatures, the chiral term may have a larger effect than the Pauli coupling of electron spins to a magnetic field. We present a model which explicitly demonstrates this. The ground state is a singlet with a gap; hence the spin susceptibility is zero while the chiral susceptibility is finite and paramagnetic.