Elementary excitations of S=1/2 one-dimensional antiferromagnet KCuGaF6 in magnetic field and quantum sine-Gordon model

TL;DR

This study investigates the elementary excitations in the one-dimensional S=1/2 antiferromagnet KCuGaF6 under magnetic fields, demonstrating their description by the quantum sine-Gordon model through ESR measurements and susceptibility analysis.

Contribution

It provides experimental validation of the quantum sine-Gordon model in KCuGaF6 and links the resonance modes to the induced staggered magnetic field and Dzyaloshinsky-Moriya interaction.

Findings

Observation of multiple resonance modes including solitons and breathers

Resonance conditions match quantum sine-Gordon model predictions

Correlation between Curie term and proportional coefficient c_s

Abstract

Elementary excitations of the S=1/2 one-dimensional Heisenberg antiferromagnet KCuGaF$_6$ with exchange constant $J/k_B$=103 K were investigated by high-frequency ESR measurements combined with a pulsed high magnetic field. When an external magnetic field H is applied in KCuGaF$_6$, a staggered magnetic field h is induced perpendicular to H owing to the staggered g tensor and the Dzyaloshinsky-Moriya (DM) interaction with an alternating D vector. Consequently, KCuGaF$_6$ in a magnetic field is represented by the quantum sine-Gordon (SG) model. We observed many resonance modes including a soliton resonance, breathers, interbreather transitions and two-breather excitation. Their resonance conditions are beautifully described by the quantum SG field theory with one adjustable parameter $c_ s=h/H$. To investigate the relationship between the Curie term due to the DM interaction and the proportional coefficient $c_s$, magnetic susceptibility measurements were also performed varying the external field direction.