Longitudinal and Transverse Zeeman Ladders in the Ising-Like Chain Antiferromagnet BaCo2V2O8

TL;DR

This study uncovers unique Zeeman ladder excitations in BaCo2V2O8, revealing how quantum spin dynamics and confinement effects manifest in a weakly coupled Ising-like antiferromagnetic chain.

Contribution

It demonstrates the observation of longitudinal Zeeman ladder modes in BaCo2V2O8, a phenomenon linked to quantum fluctuations and spinon confinement not previously documented in this material.

Findings

Identification of transverse and longitudinal Zeeman ladders

Longitudinal modes related to quantum zero-point fluctuations

BaCo2V2O8 fulfills conditions for observing these excitations

Abstract

We explore the spin dynamics emerging from the N\'eel phase of the chain compound antiferromagnet BaCo2V2O8. Our inelastic neutron scattering study reveals unconventional discrete spin excitations, so called Zeeman ladders, understood in terms of spinon confinement, due to the interchain attractive linear potential. These excitations consist in two interlaced series of modes, respectively with transverse and longitudinal polarization. The latter have no classical counterpart and are related to the zero-point fluctuations that weaken the ordered moment in weakly coupled quantum chains. Our analysis reveals that BaCo2V2O8, with moderate Ising anisotropy and sizable interchain interactions, remarkably fulfills the conditions necessary for the observation of these longitudinal excitations.