Spinons and helimagnons in the frustrated Heisenberg chain

TL;DR

This study combines analytical and numerical methods to analyze the dynamical spin structure factor in a frustrated Heisenberg chain, revealing spinon and helimagnon excitations and clarifying the nature of magnetic couplings in LiCuVO4.

Contribution

It provides the first combined bosonization and DMRG analysis of S(q,w) in a frustrated chain, clarifying excitation spectra and magnetic interactions.

Findings

Identified two spinon branches with different velocities.

Observed development of helimagnons at high energies near ferromagnetic phase.

Reinterpreted neutron scattering data, supporting a dominant ferromagnetic coupling J1/J2 ~ -2.

Abstract

We investigate the dynamical spin structure factor S(q,w) for the Heisenberg chain with ferromagnetic nearest (J1<0) and antiferromagnetic next-nearest (J2>0) neighbor exchange using bosonization and a time-dependent density-matrix renormalization group algorithm. For |J1|<< J2 and low energies we analytically find and numerically confirm two spinon branches with different velocities and different spectral weights. Following the evolution of S(q,w) with decreasing J1/J2 we find that helimagnons develop at high energies just before entering the ferromagnetic phase. Furthermore, we show that a recent interpretation of neutron scattering data for LiCuVO4 in terms of two weakly coupled antiferromagnetic chains (|J_1|<< J2) is not viable. We demonstrate that the data are instead fully consistent with a dominant ferromagnetic coupling, J1/J2 ~ -2.