Atomic and inter-atomic orbital magnetization induced in SrTiO$_3$ by chiral phonons

Abstract: An unexpectedly large transient magnetization induced by circularly polarized ferroelectric phonons was recently observed in a nonmagnetic insulator SrTiO3 [Nature 628, 534 (2024)]. We use a minimal molecular orbital model to demonstrate two electronic contributions to this effect. An atomic orbital contribution arises from the pumping of orbital angular momentum of Ti by chiral motion of coordinating oxygen atoms. An additional inter-atomic contribution is associated with the transient circulating current around the oxygen atoms, resulting in efficient dressing of phonons by electron dynamics. The insights provided by our model may facilitate the development of ultrafast magnetization control and orbitronic sources.