Longitudinal Magnetic Dynamics and Dimensional Crossover in the Quasi-One-Dimensional, Spin-1/2, Heisenberg Antiferromagnet KCuF3

TL;DR

This study confirms the existence of a longitudinal magnetic mode in KCuF3, demonstrating a dimensional crossover in spin dynamics with implications for understanding quantum fluctuations and antiferromagnetic order.

Contribution

The paper provides experimental evidence for a longitudinal mode in a quasi-one-dimensional antiferromagnet, validating theoretical predictions and exploring its properties through neutron scattering.

Findings

Confirmation of the longitudinal mode in KCuF3

Broadened lineshape indicating reduced lifetime

Evidence of continuum scattering above the mode energy

Abstract

The spin dynamics of coupled spin-1/2, antiferromagnetic Heisenberg chains is predicted to exhibit a novel longitudinal mode at low energies and temperatures below the Neel temperature. This mode is a dimensional crossover effect and reveals the presence of a limited amount of long-range antiferromagnetic order co-existing with quantum fluctuations. In this paper the existence of such a mode is confirmed in the model material KCuF3 using polarized and unpolarized inelastic neutron scattering and the longitudinal polarization of the mode is definitively established. The lineshape is broadened suggesting a reduced lifetime due to decay into spin-waves. In addition the data shows evidence of continuum scattering with a lower edge greater than the longitudinal mode energy. A detailed comparison is made with theoretical predictions and experimental work on other model materials.