Energy spectrum of bound-spinons in the quantum Ising spin-chain ferromagnet

TL;DR

This paper investigates the energy spectrum of bound spinon excitations in a quantum Ising ferromagnetic chain under a magnetic field, revealing how weak confinement leads to bosonic bound states of fermionic spinons.

Contribution

It provides a perturbative calculation of the bound spinon energy spectrum in the quantum Ising chain under small magnetic fields, extending previous theoretical frameworks.

Findings

Bound spinons form bosonic bound states at small h_z.

Calculated energy spectrum using perturbative methods.

Supports Wu and McCoy's weak confinement scenario.

Abstract

We study the excitation energy spectrum in the S=1/2 ferromagnetic Ising spin chain with the easy axis z in a magnetic field h={h_x,0,h_z}. According to Wu and McCoy's scenario of weak confinement, the fermionic spinon excitations (kinks), being free at h_z = 0 in the ordered phase, are coupled into bosonic bound states at arbitrary small h_z. We calculate the energy spectrum of such excitations in the leading order in small h_z, using different perturbative methods developed for the similar problem in the Ising field theory.