Excitation hierarchy of the quantum sine-Gordon spin chain in strong magnetic field

TL;DR

This paper investigates the magnetic excitation spectrum of a quantum spin chain material under strong magnetic fields, revealing detailed excitation modes and comparing them with quantum sine-Gordon theory predictions.

Contribution

It provides the first detailed experimental mapping of excitation hierarchies in a quantum sine-Gordon spin chain in high magnetic fields, confirming theoretical predictions.

Findings

Identification of ten excitation modes in the spectrum

Observation of breather branches and soliton signatures

Good agreement with quantum sine-Gordon field theory

Abstract

The magnetic excitation spectrum of copper pyrimidine dinitrate, a material containing S=1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, and exhibiting a field-induced spin gap, is probed using submillimeter wave electron spin resonance spectroscopy. Ten excitation modes are resolved in the low-temperature spectrum, and their frequency-field diagram is systematically studied in magnetic fields up to 25 T. The experimental data are sufficiently detailed to make a very accurate comparison with predictions based on the quantum sine-Gordon field theory. Signatures of three breather branches and a soliton, as well as those of several multi-particle excitation modes are identified.