Thermodynamic Properties and Elementary Excitations in Quantum Sine-Gordon Spin System KCuGaF6

TL;DR

This study investigates the thermodynamic properties and elementary excitations in the quantum sine-Gordon spin system KCuGaF6, revealing excitation gaps and ESR modes consistent with the quantum SG model.

Contribution

It provides experimental evidence of the quantum sine-Gordon model in a real material through thermodynamic and ESR measurements, highlighting the effects of Dzyaloshinsky-Moriya interactions.

Findings

Observation of excitation gap in specific heat under magnetic field

Detection of ESR modes including soliton and breather excitations

Confirmation of quantum sine-Gordon model applicability

Abstract

Thermodynamic properties and elementary excitations in $S=1/2$ one-dimensional Heisenberg antiferromagnet KCuGaF$_6$ were investigated by magnetic susceptibility, specific heat and ESR measurements. Due to the Dzyaloshinsky-Moriya interaction with alternating $D$-vectors and/or the staggered $g$-tensor, the staggered magnetic field is induced when subjected to external magnetic field. Specific heat in magnetic field clearly shows the formation of excitation gap, which is attributed to the staggered magnetic field. The specific heat data was analyzed on the basis of the quantum sine-Gordon (SG) model. We observed many ESR modes including one soliton and three breather excitations characteristic of the quantum SG model.