Emergent cross-product-type spin-orbit coupling under ferroaxial ordering

Abstract: A ferroic alignment of a time-reversal-even axial vector, which is called the ferroaxial ordered state, is identified by the spontaneous rotational distortion of the lattice structure to break the vertical mirror symmetry. We theoretically investigate what happens in the electronic structure once the ferroaxial ordering occurs by analyzing a tetragonal d-p cluster model with transition metal oxide in mind. By adopting the symmetry-adapted multipole representation, we elucidate the emergent cross-product form of the spin-orbit coupling by the interplay between the atomic spin-orbit coupling and the d-p hybridization according to the vertical mirror symmetry breaking, which corresponds to the electronic order parameter of the ferroaxial ordering.