Theory of Low Temperature Electron Spin Resonance in Half-integer Spin Antiferromagnetic Chains

TL;DR

This paper develops a field theory-based model for low-temperature electron spin resonance in half-integer spin antiferromagnetic chains, predicting power-law behaviors and explaining experimental observations without previous approximations.

Contribution

It introduces a new theoretical approach to ESR in antiferromagnetic chains that aligns with experiments and clarifies the nature of observed ESR peaks.

Findings

Power-law line-width broadening predicted for anisotropic effects

Zero width absorption peaks occur at T -> 0 in some cases

The second ESR peak in Cu benzoate is explained as a sine-Gordon breather, not Neel order

Abstract

A theory of low temperature (T) electron spin resonance (ESR) in half-integer spin antiferromagnetic chains is developed using field theory methods and avoiding previous approximations. It is compared to experiments on Cu benzoate. Power laws are predicted for the line-width broadening due to various types of anisotropy. At T -> 0, zero width absorption peaks occur in some cases. The second ESR peak in Cu benzoate, observed at T<.76K, is argued not to indicate Neel order as previously claimed, but to correspond to a sine-Gordon "breather" excitation.