Emergence of soliton chirality in a quantum antiferromagnet

Abstract

Left- and right-handed chiral matter is present at every scale ranging from seashells to molecules to elementary particles. In magnetism, chiralitymay be inherited fromthe asymmetry of the underlying crystal structure, or it may emerge spontaneously. In particular, there has been a long-standing search for chiral spin states 1 that emerge spontaneously with the disappearance of antiferromagnetic long-range order. Here we identify a generic system supporting such a behaviour and report on experimental evidence for chirality associated with the quantum dynamics of solitons 2-5 in antiferromagnetic spin chains. The soliton chirality observed by polarized neutron scattering is in agreement with theoretical predictions and is a manifestation of a Berry phase 6 . Our observations provide the first example of the emergence of spin currents and hidden chiral order that accompany the disappearance of antiferromagnetic order, a scheme believed to lie at the heart of the enigmatic normal state of cuprate superconductors.