On the Field-Induced Gap in Cu Benzoate and Other S=1/2 Antiferromagnets

TL;DR

This paper investigates the unexpected magnetic field-induced gap in Cu benzoate, explaining it through a sine-Gordon quantum field theory derived from staggered interactions, and provides detailed theoretical analysis and predictions.

Contribution

It develops a comprehensive theoretical framework for the field-induced gap in Cu benzoate, incorporating a sine-Gordon model and detailed calculations of physical quantities.

Findings

The gap scales approximately as the 2/3 power of the magnetic field.

Exact amplitudes for gap, susceptibility, and magnetization scaling are provided.

Predictions for soliton and breather peak intensities and their temperature dependence.

Abstract

Recent experiments on the S=1/2 antiferromagnetic chain compound, Cu benzoate, discovered an unexpected gap scaling as approximately the 2/3 power of an applied magnetic field. A theory of this gap, based on an effective staggered field, orthogonal to the applied uniform field, resulting from a staggered gyromagnetic tensor and a Dzyaloshinskii-Moriya interaction, leading to a sine-Gordon quantum field theory, has been developed. Here we discuss many aspects of this subject in considerable detail, including a review of the S=1/2 chain in a uniform field, a spin-wave theory analysis of the uniform plus staggered field problem, exact amplitudes for the scaling of gap, staggered susceptibility and staggered magnetization with field or temperature, intensities of soliton and breather peaks in the structure function and field and temperature dependence of the total susceptibility.