Orbital currents, anapoles, and magnetic quadrupoles in CuO

TL;DR

This paper theoretically characterizes orbital currents in CuO, identifying two key order parameters, and provides a method to experimentally distinguish them using resonant X-ray diffraction, clarifying previous experimental claims.

Contribution

It introduces a theoretical framework describing orbital currents in CuO with two order parameters and proposes a way to experimentally differentiate them.

Findings

Orbital currents in CuO involve two order parameters: anapole and magnetic quadrupole.

Resonant X-ray diffraction can disentangle these two order parameters.

The analysis clarifies previous experimental claims of anapole detection in CuO.

Abstract

We show that orbital currents in a CuO2 plane, if present, should be described by two independent parity and time-reversal odd order parameters, a toroidal dipole (anapole) and a magnetic quadrupole. Based on this, we derive the resonant X-ray diffraction cross-section for monoclinic CuO at the antiferromagnetic wavevector and show that the two order parameters can be disentangled. From our analysis, we examine a recent claim of detecting anapoles in CuO.