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

Lingyuan Gao, Sergei Prokhorenko, Yousra Nahas, and Laurent Bellaiche

Phys. Rev. Lett. 131, 196801 – Published 9 November 2023

Abstract

Recent studies have revealed that chiral phonons resonantly excited by ultrafast laser pulses carry magnetic moments and can enhance the magnetization of materials. In this work, using first-principles-based simulations, we present a real-space scenario where circular motions of electric dipoles in ultrathin two-dimensional ferroelectric and nonmagnetic films are driven by orbital angular momentum of light via strong coupling between electric dipoles and optical field. Rotations of these dipoles follow the evolving pattern of the optical field and create strong on-site orbital magnetic moments of ions. By characterizing topology of orbital magnetic moments in each 2D layer, we identify the vortex type of topological texture—magnetic merons with a one-half topological charge and robust stability. Our study thus provides alternative approaches for generating magnetic fields and topological textures from light-matter interaction and dynamical multiferroicity in nonmagnetic materials.

Received 14 March 2023
Accepted 19 September 2023

DOI:https://doi.org/10.1103/PhysRevLett.131.196801

Physics Subject Headings (PhySH)

Light-matter interaction Magnetic texture Magnetism

Ferroelectrics Multiferroics

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Lingyuan Gao , Sergei Prokhorenko, Yousra Nahas, and Laurent Bellaiche^*

Physics Department and Institute for Nanoscience and Engineering, University of Arkansas, Fayetteville, Arkansas 72701, USA

^*Corresponding author: laurent@uark.edu

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Vol. 131, Iss. 19 — 10 November 2023

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Images

Figure 1
Illustration of ferroelectric PZT films illuminated by OV beam. (a) OV beam with a helical wavefront is normally incident on PZT films. Current loops form at each site due to the rotation of electric dipoles, which induce emergent magnetic moments (black arrows pointing up). (b) The distribution of in-plane components of local soft mode vectors $u_{x, y}$ (denoted by arrows) on each site (gray sphere) at $t = n T$ after the system establishes cyclic motion. We draw polar coordinates with its origin coinciding with the center of the (001) plane to denote the thin film plane and three circles in radius of $0.5 w$ , $w$ , and $2 w$ , colors of which indicate the variation of the $E$ field intensity along the radial direction. The bottom part depicts the change of the dipole’s orientation with time at a selected site.
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Figure 2
(a)–(d) The variation of $u_{x, y} (\vec{r}, t)$ at different sites with time. In accordance with the coordinates displayed in Fig. 1, $u_{x, y}$ associated with 6 sites on the $x$ axis of the coordinates are shown in (a),(b), while $u_{x, y}$ associated with 6 sites on the $y$ axis are shown in (c),(d). In the legend, the “ $+$ ” and “ $-$ ” signs denote whether sites are located on the positive or negative side of the axes, respectively. “ $x w$ ” ( $x = 0.5 \times, 1 \times, 2 \times$ , and $w$ is the beam radius of 7 u.c.) denotes the distance from the site to the center. $u_{x, y}$ is in the unit of lattice constant (3.99 Å as 1 u.c.). (e) The effective magnetic field generated in the PZT system illuminated by the OV beam.
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Figure 3
(a) In-plane view of the magnetic moment configuration on layer 2 at $t = 3.3 ps$ , with arbitrary units. The horizontal and vertical axes denote the site number along the $x$ and $y$ directions, respectively. In-plane arrows denote $m_{x, y}$ and the color denotes $m_{z}$ . (b) Similar to (a), but on layer 6 at $t = 3.3 ps$ . (c) Section view of the magnetic moment configuration in the $y = 40$ plane at $t = 3.3 ps$ . The horizontal and vertical axes denote the site number along the $x$ direction and the layer number along the $z$ direction, respectively. The arrows denote $m_{x}$ and $m_{z}$ components. (d) Topological charge density map $ρ_{s k}$ on layer 2 at $t = 3.3 ps$ . (e) Spherical triangles set by three orbital magnetic moments $m_{i}$ on sites (40, 40), (41, 40), and (41, 41), respectively. Vertices $S_{1}$ , $S_{2}$ , and $S_{3}$ are projections of three $m_{i}$ on the sphere. An enlarged in-plane view of these moments are presented in the inset. (f) The variation of topological number $N$ with time for each layer during 3–4 ps.
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