Bound states of magnons in the S=1/2 quantum spin ladder

TL;DR

This paper investigates the excitation spectrum of a two-leg S=1/2 Heisenberg ladder, revealing the existence of bound states of magnons using a quasiparticle approach treating excitations as a dilute Bose gas.

Contribution

It introduces a novel method to analyze bound states of magnons in quantum spin ladders by modeling excitations as a dilute Bose gas with strong repulsion.

Findings

Identification of singlet and triplet two-particle bound states

Bound states are shown to be a general feature in dimerized quantum spin models

The approach provides a framework for understanding excitation spectra in quantum spin systems

Abstract

We study the excitation spectrum of the two-leg antiferromagnetic S=1/2 Heisenberg ladder. Our approach is based on the description of the excitations as triplets above a strong-coupling singlet ground state. The quasiparticle spectrum is calculated by treating the excitations as a dilute Bose gas with infinite on-site repulsion. We find singlet (S=0) and triplet (S=1) two-particle bound states of the elementary triplets. We argue that bound states generally exist in any dimerized quantum spin model.