A modified triplet-wave expansion method applied to the alternating Heisenberg chain

TL;DR

This paper introduces a modified triplet-wave expansion method for dimerized spin systems, applied to the alternating Heisenberg chain, offering a new approach that avoids constraint equations and compares favorably with existing methods.

Contribution

The paper presents a novel modification of the triplet-wave expansion formalism using projection operators, improving the analysis of dimerized spin systems like the alternating Heisenberg chain.

Findings

The method accurately reproduces known results for the alternating Heisenberg chain.

It provides insights into quasiparticle breakdown in two-triplon bound states.

Comparisons show good agreement with dimer series expansions and exact diagonalization.

Abstract

An alternative triplet-wave expansion formalism for dimerized spin systems is presented, a modification of the 'bond operator' formalism of Sachdev and Bhatt. Projection operators are used to confine the system to the physical subspace, rather than constraint equations. The method is illustrated for the case of the alternating Heisenberg chain, and comparisons are made with the results of dimer series expansions and exact diagonalization. Some discussion is included of the phenomenon of 'quasiparticle breakdown', as it applies to the two-triplon bound states in this model.