Inter-site Coulomb interaction and Heisenberg exchange

TL;DR

This paper investigates how inter-site Coulomb interactions influence magnetic exchange interactions in insulators, revealing that direct exchange is enhanced while superexchange is suppressed, affecting the realization of t-J models.

Contribution

It demonstrates the contrasting effects of inter-site Coulomb repulsion on direct and superexchange interactions using exact diagonalization, highlighting conditions for large J values.

Findings

Direct exchange constant J is enhanced by inter-site Coulomb interaction.

Superexchange constant J is suppressed by inter-site Coulomb interaction.

Strong inter-site repulsion near CDW instability can produce large J in models.

Abstract

Based on exact diagonalization results for small clusters we discuss the effect of inter-site Coulomb repulsion in Mott-Hubbard or charge transfer insulators. Whereas the exchange constant J for direct exchange is substantially enhanced by inter-site Coulomb interaction, that for superexchange is suppressed. The enhancement of J in the single-band models holds up to the critical value for the charge density wave (CDW) instability, thus opening the way for large values of J. Single-band Hubbard models with sufficiently strong inter-site repulsion to be near a CDW instability thus may provide `physical' realizations of t-J like models with the `unphysical' parameter ratio J/t=1.