Dynamic Spin Correlation Function of the Alternating Spin-1/2 Antiferromagnetic Chain with Competing Interactions

TL;DR

This paper investigates the dynamic spin correlation function of an alternating spin-1/2 antiferromagnetic chain with competing interactions, revealing bound states and unique wavevector dependencies, and relates findings to experimental neutron scattering data.

Contribution

It provides a detailed numerical analysis of the correlation function in a complex spin chain, highlighting features due to dimer order and comparing with experimental results.

Findings

Observation of a singlet-triplet gap and bound triplet states

Distinct wavevector dependence of bound state intensity

Agreement with neutron scattering experiments on CuGeO3

Abstract

Dynamic spin correlation function of the $S=1/2$ antiferromagnetic spin chain with alternating nearest neighbor and competing next nearest neighbor interactions is studied using the numerical diagonalization method. We find characteristics of the correlation function, which are the consequence of the dimer order in the ground state: (1) A typical singlet-triplet gap is observed and such a lowest-energy triplet state is found to form a bound state, showing strong peaks below a continuum band with weak but distinct upper and lower boundaries. (2) The intensity of the bound state shows a quite different wavevector-dependence from that of the corresponding intensity at the lower boundary in the usual antiferromagnet. These features are examined by the variational calculation and are favorably discussed in connection with recent experimental results of neutron inelastic scattering in the inorganic spin-Peierls system, CuGeO$_3$.