Neutron scattering by magnetic octupoles of a quantum liquid

TL;DR

This paper reports the first observation of neutron scattering primarily influenced by magnetic octupoles in a quantum spin ice, revealing a new type of quantum spin liquid with distinctive experimental signatures.

Contribution

It introduces a novel experimental signature of magnetic octupoles in neutron scattering within a quantum spin liquid, expanding the understanding of multipolar effects in quantum materials.

Findings

Neutrons diffract mainly by magnetic octupoles in a quantum spin ice.

Electronic wavefunction becomes octupolar due to correlations.

Discovery of a new quantum spin liquid with unique neutron scattering signature.

Abstract

Neutron scattering is a powerful tool to study magnetic structures and dynamics, benefiting from a precisely established theoretical framework. The neutron dipole moment interacts with electrons in materials via their magnetic field, which can have spin and orbital origins. Yet in most experimentally studied cases the individual degrees of freedom are well described within the dipole approximation, sometimes accompanied by further terms of a multipolar expansion that usually act as minor corrections to the dipole form factor. Here we report a unique example of neutrons diffracted mainly by magnetic octupoles. This unusual situation arises in a quantum spin ice where the electronic wavefunction becomes essentially octupolar under the effect of correlations. The discovery of such a new type of quantum spin liquid that comes with a specific experimental signature in neutron scattering is remarkable, because these topical states of matter are notoriously difficult to detect.