Thermodynamic properties of quantum sine-Gordon spin chain system KCuGaF6

TL;DR

This study explores the thermodynamic behavior of the quantum sine-Gordon spin chain system KCuGaF6 under magnetic fields, revealing field-induced gaps and phase transitions, with results aligning with quantum SG theory in certain directions.

Contribution

It provides experimental validation of quantum sine-Gordon model predictions for KCuGaF6 and identifies deviations in some field orientations, highlighting complex excitation modes.

Findings

Field-induced energy gaps increase with magnetic field strength.

Quantum phase transition observed between gapless and gapped states.

Quantum SG model describes thermodynamics well for H // c direction.

Abstract

We investigated the thermodynamic properties of the spin-1/2 one-dimensional Heisenberg antiferromagnet KCuGaF6 by measuring the specific heat in magnetic fields. When this compound is subjected to a uniform magnetic field H a transverse staggered magnetic field h is induced in this compound owing to the staggered component of the g tensor and the Dzyaloshinskii-Moriya interaction with an alternating D vector. Consequently, the quantum sine-Gordon (SG) model is an effective model of this compound in a uniform magnetic field. In three different field directions, we observed a magnetic-field-induced gap, which increases with H. We analyzed experimental results using specific heat theory based on quantum SG theory. The thermodynamic property for H // c is very well described in terms of the elementary excitations characteristic of the quantum SG model, while for the other field directions, significant contributions from other excitation modes beyond the framework of the quantum SG model were observed. For H // b, a quantum phase transition between gapless and gapped ground states was observed.