Ferromagnetism in a hard-core boson model

TL;DR

This paper investigates ferromagnetism in a hard-core boson model, revealing that ferromagnetic ground states are stable for bosons across all hole densities, unlike fermions which exhibit instabilities.

Contribution

It demonstrates that in a hard-core lattice model, bosonic particles can sustain stable ferromagnetism regardless of hole density, contrasting with fermionic behavior.

Findings

Bosons exhibit stable ferromagnetism at all hole densities.

Fermions show instabilities in ferromagnetic states at finite hole densities.

The particle statistics critically influence ferromagnetic ground states.

Abstract

The problem of ferromagnetism -- associated with a ground state with maximal total spin -- is discussed in the framework of a hard-core model, which forbids the occupancy at each site with more than one particle. It is shown that the emergence of ferromagnetism on finite square lattices crucially depends on the statistics of the particles. Fermions (electrons) lead to the well-known instabilities for finite hole densities, whereas for bosons (with spin) ferromagnetism appears to be stable for all hole densities.