Dynamical Multiferroicity and Magnetic Topological Structures Induced by Orbital Angular Momentum of Light in a Non-Magnetic Material

Many efforts have been made in studying effective magnetization resulting from the temporally varying electric polarization [1, 2]. Such dynamical polarization can be produced by driving collective motions of ions, usually termed as “phonons” in solid-state language. Moreover, numerous recent studies show that light can control the magnetization in crystals by driving optical phonon modes and tuning structural distortions [3-6]. At the zone center of reciprocal space, infrared (IR)- and Raman-active modes, related to electric polarization and polarizability, respectively, can be excited with an ultrafast Terahertz (THz) laser pulse.<br/><br/>In this Talk, we will present an alternative approach to induce effective magnetic field established on the mechanism of dynamical multiferroicity. Instead of focusing on coherently excited chiral phonons, we drive real-space circular motions of ions with a particular type of light–optical vortex (OV) beam. Such light carries an orbital angular momentum (OAM) [7-9], and can manipulate the motion of microparticles as an optical tweezer [10-12]. As a prototype example, we use first-principles-based simulations and demonstrate that in ultrathin ferroelectric Pb(Zr, Ti)O₃ films, microscopic electric dipoles indeed rotate with the time-varying OAM field. As a result, orbital magnetic moments of ions are effectively generated resulting in a non-negligible magnetic field even in non-magnetic materials. More intriguingly, we will show that the microscopic magnetic moments on a single layer of this quasi 2D system are arranged in a vortex-type configuration, proving that topological magnetic structures—magnetic merons—can also be produced out of orbital magnetic moments of ions and dynamical multiferroicity.<br/><br/>The authors acknowledge the support from the Grant MURI ETHOS W911NF-21-2-0162 from Army Research Office (ARO) and the Vannevar Bush Faculty Fellowship (VBFF) Grant No. N00014-20-1-2834 from the Department of Defense. We also acknowledge the computational support from the Arkansas High Performance Computing Center for computational resources.<br/><br/><br/>References:<br/>[1] D. M. Juraschek <i>et al.</i>, Physical Review Materials 1, 014401 (2017)<br/>[2] D. M. Juraschek <i>et al.</i>, Physical Review Materials 3, 064405 (2019)<br/>[3] T.F. Nova <i>et al.</i>, Nature Physics 13, 132 (2017)<br/>[4] D. Afanasiev <i>et al.</i>, Nature materials 20, 607 (2021)<br/>[5] A. Stupakiewicz <i>et al.</i>, Nature Physics 17, 489 (2021)<br/>[6] M. Basini <i>et al.</i>, arXiv:2210.01690 (2022)<br/>[7] L. Allen <i>et al.</i>, Physical Review A 45, 8185 (1992)<br/>[8] S. Franke-Arnold, Nature Review Physics 4, 361 (2022)<br/>[9] G. F. Q. Rosen <i>et al.</i>, Review of Modern Physics 94, 035003 (2022)<br/>[10] L. Paterson <i>et al.</i>, Science 292, 912 (2001)<br/>[11] M. P. MacDonald <i>et al.</i>, Science 296, 1101 (2002)<br/>[12] D. G. Grier, Nature 424, 810 (2003)