Multi-magnon bound states in easy-axis ferromagnetic zigzag spin chain

TL;DR

This paper investigates the excitation spectrum of a frustrated spin-1/2 chain with anisotropic ferromagnetic and antiferromagnetic interactions, revealing multi-magnon bound states that influence low-temperature magnetic properties.

Contribution

It identifies and characterizes multi-magnon bound states in a frustrated ferromagnetic zigzag chain, combining analytical and numerical methods.

Findings

Existence of multi-magnon bound states in the excitation spectrum

Bound states significantly affect low-temperature susceptibility

Energy estimates of bound states using perturbation theory and numerics

Abstract

The frustrated spin-1/2 chain with weakly anisotropic ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor exchanges is studied. We focus on the excitation spectrum and the low-temperature thermodynamics in the ferromagnetic region of the ground state phase diagram. It is shown that the excitation spectrum of the model is characterized by the existence of the multi-magnon bound states. These excitations determine the low-temperature magnetic susceptibility. The energy of the bound magnon complexes is found using the scaling estimates of the perturbation theory and numerical calculations. The relation of the considered model to the edge-sharing cuprate $Li_2CuO_4$ is discussed.