Integrable models of interacting quantum spins with competing interactions

TL;DR

This paper introduces exactly solvable quantum spin models with competing interactions, revealing new phases and phenomena such as order from disorder, by combining Heisenberg subsystems with long-range Lieb-Mattis coupling.

Contribution

It presents a new class of integrable quantum spin models with coupled subsystems, enabling the study of frustration effects and complex phase diagrams.

Findings

Complete ground-state phase diagram for antiferromagnetic chain

Full thermodynamic phase diagram for the models

Discovery of a novel order-from-disorder phase

Abstract

We present a class of exactly solvable quantum spin models which consist of two Heisenberg-subsystems coupled via a long-range Lieb-Mattis interaction. The total system is exactly solvable whenever the individual subsystems are solvable and allows to study the effects of frustration. We consider (i) the antiferromagnetic linear chain and (ii) the Lieb-Mattis antiferromagnet for the subsystem-Hamiltonians and present (i) the complete ground-state phase diagram and (ii) the full thermodynamic phase diagram. We find a novel phase which exhibits {\it order from disorder} phenomena.