Bond-operators and triplon analysis for spin-S dimer antiferromagnets

TL;DR

This paper develops a mean-field triplon analysis for spin-S dimer antiferromagnets, extending bond-operator theory beyond spin-1/2 and exploring phase behavior and ground states in frustrated systems.

Contribution

It introduces a generalized mean-field triplon approach for arbitrary spin-S systems, including extensions to quintet states and plaquette representations, broadening the applicability of bond-operator methods.

Findings

Quantum dimerized phases can persist at large spin values under frustration.

The method effectively analyzes phase diagrams of coupled-dimer models on square and honeycomb lattices.

Extensions to include higher total-spin states are feasible and demonstrated.

Abstract

The mean-field triplon analysis is developed for spin-S quantum antiferromagnets with dimerized ground states. For the spin-1/2 case, it reduces to the well known bond-operator mean-field theory. It is applied to a coupled-dimer model on square lattice, and to a model on honeycomb lattice with spontaneous dimerization in the ground state. Different phases in the ground state are investigated as a function of spin. It is found that under suitable conditions (such as strong frustration) a quantum ground state (dimerized singlet phase in the present study) can survive even in the limit $S\rightarrow \infty$. Two quick extensions of this representation are also presented. In one case, it is extended to include the quintet states. In another, a similar representation is worked out on a square plaquette. A convenient procedure for evaluating the total-spin eigenstates for a pair of quantum spins is presented in the appendix.