Emergent chirality in a polar meron to skyrmion phase transition

Yu-Tsun Shao; Sujit Das; Zijian Hong; Ruijuan Xu; Swathi Chandrika; Fernando Gómez-Ortiz; Pablo García-Fernández; Long-Qing Chen; Harold Y Hwang; Javier Junquera; Lane W Martin; Ramamoorthy Ramesh; David A Muller

doi:10.1038/s41467-023-36950-x

Emergent chirality in a polar meron to skyrmion phase transition

Nat Commun. 2023 Mar 13;14(1):1355. doi: 10.1038/s41467-023-36950-x.

Authors

Yu-Tsun Shao^{1

2}, Sujit Das^{3

4}, Zijian Hong^{5

6}, Ruijuan Xu^{7

8

9}, Swathi Chandrika¹, Fernando Gómez-Ortiz¹⁰, Pablo García-Fernández¹⁰, Long-Qing Chen⁵, Harold Y Hwang^{7

8}, Javier Junquera¹⁰, Lane W Martin^{3

11}, Ramamoorthy Ramesh^{4

11

12

13}, David A Muller^{14

15}

Affiliations

¹ School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA.
² Mork Family Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, CA, USA.
³ Department of Materials Science and Engineering, University of California, Berkeley, CA, USA.
⁴ Materials Research Centre, Indian Institute of Science, Bangalore, India.
⁵ Materials Research Institute and Department of Materials Science and Engineering, The Pennsylvania State University, University Park, PA, USA.
⁶ Laboratory of Dielectric Materials, School of Materials Science and Engineering, Zhejiang University, Hangzhou, 310027, China.
⁷ Department of Applied Physics, Stanford University, Stanford, CA, USA.
⁸ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, Menlo Park, CA, USA.
⁹ Department of Materials Science and Engineering, North Carolina State University, Raleigh, NC, USA.
¹⁰ Departamento de Ciencias de la Tierra y Física de la Materia Condensada, Universidad de Cantabria, Cantabria Campus Internacional, Avenida de los Castros s/n, 39005, Santander, Spain.
¹¹ Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, USA.
¹² Department of Physics, University of California, Berkeley, CA, USA.
¹³ Rice University, Houston, TX, USA.
¹⁴ School of Applied and Engineering Physics, Cornell University, Ithaca, NY, USA. david.a.muller@cornell.edu.
¹⁵ Kavli Institute at Cornell for Nanoscale Science, Ithaca, NY, USA. david.a.muller@cornell.edu.

Abstract

Polar skyrmions are predicted to emerge from the interplay of elastic, electrostatic and gradient energies, in contrast to the key role of the anti-symmetric Dzyalozhinskii-Moriya interaction in magnetic skyrmions. Here, we explore the reversible transition from a skyrmion state (topological charge of -1) to a two-dimensional, tetratic lattice of merons (with topological charge of -1/2) upon varying the temperature and elastic boundary conditions in [(PbTiO₃)₁₆/(SrTiO₃)₁₆]₈ membranes. This topological phase transition is accompanied by a change in chirality, from zero-net chirality (in meronic phase) to net-handedness (in skyrmionic phase). We show how scanning electron diffraction provides a robust measure of the local polarization simultaneously with the strain state at sub-nm resolution, while also directly mapping the chirality of each skyrmion. Using this, we demonstrate strain as a crucial order parameter to drive isotropic-to-anisotropic structural transitions of chiral polar skyrmions to non-chiral merons, validated with X-ray reciprocal space mapping and phase-field simulations.

Abstract

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