Orbital moment generation by circularly polarized phonons in strontium titanate

A recent observation by Basini [Nature 628, 534 (2024)] of a large transient magnetization induced by circularly polarized ferroelectric phonons in SrTiO3 suggests the existence of hitherto unrecognized mechanisms coupling chiral lattice dynamics with electric degrees of freedom. Here, we develop an atomistic tight-binding model demonstrating a possible contribution to this effect arising from the pumping of atomic electron orbital angular momentum of Ti by chiral motion of oxygen atoms coordinating it, and facilitated by the degeneracy of its t2g orbitals allowing unquenched transient orbital moments. The proposed mechanism may be relevant to other materials with orbitally degenerate or quasi-degenerate electron states, and is attractive for efficient orbital moment generation in orbitronic applications without electric currents.