Accurate mapping of quantum Heisenberg magnetic models of spin $s$ on strong-coupling magnon systems

TL;DR

This paper introduces an infinite-U term into the magnon Hamiltonian of quantum Heisenberg models to eliminate unphysical states, resulting in more accurate and physically consistent descriptions of magnetic properties.

Contribution

The authors develop a strong-coupling magnon Hamiltonian with an infinite-U term that automatically truncates unphysical states, improving the accuracy over previous models.

Findings

Elimination of unphysical spin wave states on each site.

Reproduction of sublattice magnetizations with improved spectral weight.

Lower ground-state energies compared to previous approximations.

Abstract

An infinite-$U$ term is introduced into the Holstein-Primakoff-transformed magnon hamiltonian of quantum Heisenberg magnetic models of spin $s$. This term removes the unphysical spin wave states on every site and truncates automatically the expansion in powers of the magnon occupation operator. The resultant strong-coupling magnon hamiltonians are accurately equivalent to the original spin hamiltonians. The on-site $U$ levels and their implications are studied. Within a simple decoupling approximation for our strong-coupling magnon models we can easily reproduce the results for the (sublattice) magnetizations obtained previously for the original spin model. But our bosonic hamiltonians without any unphysical states allow for substantially improved values for the spectral weight in the ground state and for lower ground-state energies than those obtained within previous approximations.