Theory of the field-induced gap in $S=1/2$ antiferromagnetic chains

TL;DR

This paper explains how an external magnetic field induces a gap in the excitation spectrum of $S=1/2$ antiferromagnetic chains, primarily due to effective staggered fields from anisotropic interactions, supported by neutron scattering data.

Contribution

It introduces a theoretical framework linking the field-induced gap to staggered fields from the g-tensor and Dzyaloshinskii-Moriya interaction in $S=1/2$ chains.

Findings

The gap depends on the applied magnetic field as explained by the model.

Identification of peaks in the structure factor $S(q,)$ related to the gap.

Validation of the theory with neutron scattering experiments.

Abstract

In a recent neutron-scattering experiment on the quasi-one-dimensional $S=1/2$ antiferromagnet Cu Benzoate, a gap was induced by an applied magnetic field. We argue that the primary mechanism of the gap formation is an effective staggered field due to both the alternating $g$-tensor and the Dzyaloshinskii-Moriya interaction. We explain the dependence of the gap on the applied field, as well as identify several peaks in the structure factor $S(q,\omega)$.