Dynamics of an anisotropic Haldane antiferromagnet in strong magnetic field

TL;DR

This study investigates the behavior of an anisotropic Haldane antiferromagnet under strong magnetic fields using neutron scattering, revealing gap closure and reopening phenomena and validating a specific theoretical model.

Contribution

It provides experimental data on the field-dependent magnon modes in an anisotropic Haldane chain and confirms the accuracy of a recent theoretical model.

Findings

Haldane gap closes at ~4T and reopens at higher fields.

Experimental magnon mode behavior matches the predictions of Zheludev et al.'s model.

Only the recent theoretical model accurately describes the observed phenomena.

Abstract

We report the results of elastic and inelastic neutron scattering experiments on the Haldane gap quantum antiferromagnet Ni(C5D14N2)2N3(PF6) performed at mK temperatures in a wide range of magnetic field applied parallel to the S = 1 spin chains. Even though this geometry is closest to an ideal axially symmetric configuration, the Haldane gap closes at the critical field Hc~4T, but reopens again at higher fields. The field dependence of the two lowest magnon modes is experimentally studied and the results are compared with the predictions of several theoretical models. We conclude that of several existing theories, only the recently proposed model [Zheludev et al., cond-mat/0301424 ] is able to reproduce all the features observed experimentally for different field orientations.