Quasiparticles of string solutions in the spin-1/2 antiferromagnetic Heisenberg chain in a magnetic field

TL;DR

This paper investigates the spectral properties of the spin-1/2 antiferromagnetic Heisenberg chain in a magnetic field using Bethe-ansatz solutions, highlighting the roles of quasiparticles like psinon, antipsinon, and 2-string in dynamical behaviors.

Contribution

It introduces the significance of a 2-string quasiparticle in the dynamical properties and continuum formation in a magnetic field, extending understanding beyond traditional quasiparticles.

Findings

Identification of a 2-string quasiparticle's role in the continuum.

Continuum's evolution from zero-field to high-field regimes.

Confirmation of theoretical results with experimental data on CuCl2·2N(C5D5).

Abstract

Spectral properties of the spin-1/2 antiferromagnetic Heisenberg chain in a magnetic field are investigated by using exact Bethe-ansatz solutions. We argue that not only quasiparticles called psinon and antipsinon but also a quasiparticle representing a 2-string in the Bethe ansatz plays an important role for dynamical properties in a magnetic field. Combined with psinon and antipsinon, the quasiparticle for a 2-string forms a continuum in the high-energy regime for transverse dynamical structure factor $S^{+-}(k,\omega)$. In the zero-field limit, the continuum is located on the mode of the lowest excited states in zero field called the des Cloizeaux-Pearson mode. In a magnetic field, the continuum separates from other low-energy continua, and reduces to the mode of bound states of overturned spins from the fully polarized state near the saturation field. We confirm the relevance through comparisons with available experimental results on the quasi-one-dimensional antiferromagnet CuCl$_2\cdot$2N(C$_5$D$_5$).