Ferromagnetic response of a "high-temperature" quantum antiferromagnet

TL;DR

This study investigates how ionic potential influences antiferromagnetic order in a quantum antiferromagnet, revealing a transition to ferromagnetic-like behavior in dynamic response despite static antiferromagnetic order.

Contribution

It uncovers the dual role of ionic potential in modulating antiferromagnetic order and demonstrates a dynamic ferromagnetic response in a static antiferromagnet.

Findings

Small ionic potential increases Neel temperature.

Large ionic potential suppresses antiferromagnetism via resonance effects.

Dynamic response mimics ferromagnetic behavior.

Abstract

We study the finite temperature antiferromagnetic phase of the ionic Hubbard model in the strongly interacting limit using quantum Monte Carlo based dynamical mean field theory. We find that the ionic potential plays a dual role in determining the antiferromagnetic order. A small ionic potential (compared to Hubbard repulsion) increases the super-exchange coupling in the projected sector of the model, leading to an increase in the Neel temperature of the system. A large ionic potential leads to resonance between projected antiferromagnetically ordered configurations and density ordered configurations with double occupancies, thereby killing antiferromagnetism in the system. This novel way of degrading antiferromagnetism leads to spin polarization of the low energy single particle density of states. The dynamic response of the system thus mimics ferromagnetic behaviour, although the system is still an antiferromagnet in terms of the static spin order.