Dimer phases in quantum antiferromagnets with orbital degeneracy

TL;DR

This paper investigates the ground states of orbitally degenerate quantum magnets, revealing how Hund's coupling influences dimer formations and lifts degeneracy via an order-out-of-disorder mechanism.

Contribution

It introduces a microscopic model for orbitally degenerate quantum magnets and demonstrates how Hund's coupling affects dimer ground states and degeneracy lifting.

Findings

Ground-state manifold is spanned by dimer coverings at zero Hund's coupling.

Finite Hund's coupling lifts degeneracy through virtual triplet excitations.

Relevance to experimentally studied systems is discussed.

Abstract

We study and solve the ground-state problem of a microscopic model for a family of orbitally degenerate quantum magnets. The orbital degrees of freedom are assumed to have directional character and are represented by static Potts-like variables. In the limit of vanishing Hund's coupling, the ground-state manifold of such a model is spanned by the hard-core dimer (spin singlet) coverings of the lattice. The extensive degeneracy of dimer coverings is lifted at a finite Hund's coupling through an order-out-of-disorder mechanism by virtual triplet excitations. The relevance of our results to several experimentally studied systems is discussed.