Orbital currents in CuO

We developed a scheme to investigate parity and time-reversal-odd order parameters associated with orbital currents within the framework of first-principle calculations. By applying our approach on CuO we further explore the source of orbital currents in this material which where observed by resonant x-ray diffraction. The comparison of our calculation with the experimental measurements revealed that orbital currents in CuO are “antiferro”-ordered spin toroidal moments. Our analysis shows that these moments originate from a strong hybridization between Cu-dz orbitals with neighboring O-p orbitals. This interaction enforces a spin asymmetry around Cu, which creates toroidal moments. Moreover, our investigations revealed that several parity and time-reversal odd multipole orders coexist in CuO. In addition to the “antiferro” spin toroidal moment an “antiferro”magnetoelectric monopolar ordering with a different ordering vector is found. Finally, we discuss the possibility of using our approach to identify orbital currents in other materials.