Neutron scattering by Dirac multipoles

TL;DR

This paper investigates how Dirac multipoles, which are magnetic and polar, influence neutron scattering in materials like high-Tc superconductors and iridates, revealing universal aspects of magnetic charge and excitation selection rules.

Contribution

It introduces the construction of Dirac quadrupoles in centrosymmetric sites and derives selection rules for neutron inelastic scattering and RIXS, applicable beyond specific materials.

Findings

Dirac multipoles contribute to neutron scattering signals.

Selection rules for excitations are established for neutron inelastic scattering.

Simulation of neutron diffraction in Sr2IrO4 demonstrates the universal applicability.

Abstract

Ordered magnetic charge created by Dirac multipoles that are magnetic and polar is examined. It has previously been revealed in the pseudo-gap phase of high-Tc materials by use of the Kerr effect and magnetic neutron Bragg diffraction. There are several forms of the polar operator for magnetic neutron scattering built from spin and electric dipole operators of unpaired electrons. Construction of Dirac quadrupoles that emerge from centrosymmetric sites used by Cu ions in the ceramic superconductor Hg1201 is illustrated, together with selection rules for excitations that will feature in neutron inelastic scattering, and RIXS experiments. Most reported expressions and results have universal value, because they are not specific to ceramic superconductors. To illustrate this aspect of our work we simulate neutron diffraction from a magnetically ordered iridate (Sr2IrO4).