Quantum critical behavior driven by Hund's rule coupling in quantum antiferromagnets

TL;DR

This paper investigates how Hund's rule coupling induces quantum critical behavior and complex magnetic phases in a two-orbital antiferromagnetic model on a square lattice, revealing a rich phase diagram including ordered and disordered states.

Contribution

It introduces a spin-wave theory analysis of Hund's rule coupling effects, identifying a quantum phase diagram with four distinct magnetic regions in a two-orbital model.

Findings

Identification of four magnetic phases including quantum-disordered state

Discovery of a canted magnetic order driven by Hund's rule coupling

Relevance to Fe-pnictide antiferromagnets

Abstract

When localized spins on different d orbitals prefer different types of antiferromagnetic ordering, the Hund's rule coupling creates frustration. Using spin-wave theory we study the case of two such orbitals on a square lattice coupled through Hund's rule, such that the first one couples antiferromagnetically (AF) more strongly to its nearest neighbors, while the second couples more strongly to its next nearest neighbors. We find that the zero temperature phase diagram has four regions, one characterized by the familiar $(\pi,\pi)$ AF order, a second by the columnar $(\pi,0)$ order, a third by a {\it canted} order and a fourth region where a quantum-disordered state emerges. We comment on the possible relevance of these findings for the case of Fe-pnictide based antiferromagnets.