Elementary excitations and specific heat in quantum sine-Gordon spin chain KCuGaF6

TL;DR

This study investigates elementary excitations in the quantum sine-Gordon model within a specific antiferromagnetic chain material, revealing field-induced gaps and excitations consistent with theoretical predictions through specific heat and ESR measurements.

Contribution

It provides experimental evidence of solitons and breathers in a quantum sine-Gordon system, directly observing q=0 excitations via ESR, and confirms the theoretical model with real material data.

Findings

Field-induced gap observed in specific heat measurements.

Direct ESR detection of solitons and breathers.

Experimental results align with quantum sine-Gordon theory.

Abstract

Elementary excitations of an S = 1/2 antiferromagnetic Heisenberg chain KCuGaF6 were investigated through specific heat and electron spin resonance (ESR) measurements. In this compound, a staggered field is induced perpendicular to the external field because of the alternating g tensor and the Dzyaloshinsky-Moriya interaction with an alternating D vector. Such a spin system can be mapped onto the quantum sine-Gordon (SG) model, when subjected to the external magnetic field. Specific heat shows clear evidence of the field-induced gap, which is related to the elementary excitations, solitons and breathers, characteristic of the quantum SG model. q = 0 excitations originated from solitons and breathers were directly observed by high-frequency high-field ESR. These experimental results are well described by the quantum SG field theory.