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Local negative permittivity and topological-phase transition in polar skyrmions



Sujit Das, Zijian Hong, Vladimir Stoica, Mauro A. Goncalves, Yu-Tsun Shao, Eric Parsonnet, Eric J. Marksz, Sahar Saremi, Margaret McCarter, A Reynoso, Christian J. Long, Aaron M. Hagerstrom, D Meyers, V Ravi, B Prasad, H Zhou, Z Zhang, H Wen, F Gomez-Ortiz, P Garcia-Fernandez, J Bokor, J Iniguez, J Freeland, Nathan D. Orloff, J Junquera, Long-Qing Chen, Sayeef Salahuddin, David A. Muller, L Martin, R. Ramesh


Topological solitons such as magnetic skyrmions have drawn enormous attention as stable quasi- particle-like objects. The recent discovery of polar vortices and skyrmions in ferroelectric- oxide superlattices, exhibiting exotic physical phenomena, has opened up new vistas to explore topology, emergent phenomena, and approaches for manipulating such features with electric fields. , Using macroscopic dielectric measurements, coupled with direct scanning convergent- beam electron diffraction (SCBED) imaging of the local polarization and electric-field profiles at the atomic scale, theoretical phase-field simulations, and second-principles calculations, we demonstrate that polar skyrmions in (PbTiO3)n/(SrTiO3)n superlattices are distinguished by a sheath of negative permittivity at the periphery of each skyrmion. This enables a strong enhancement of the effective dielectric permittivity as compared to individual SrTiO3 and PbTiO3 layers. Moreover, the response of these topologically protected structures to electric field and temperature reveal a reversible phase transition from a topologically protected skyrmion state (with a topological charge of +1) to a trivial uniform ferroelectric state (topological charge of 0), accompanied by a large tunability of the dielectric permittivity. Pulsed-switching measurements show a time-dependent evolution and recovery of the skyrmion state (and the macroscopic dielectric response). The interrelationship between the topological and the dielectric properties presents a unique opportunity to simultaneously manipulate both of both of them by a single, and easily controlled, stimulus, the applied electric field.
Nature Materials


polar, skyrmion, ferroelectric, negative, permittivity, thin films


Das, S. , Hong, Z. , Stoica, V. , Goncalves, M. , Shao, Y. , Parsonnet, E. , Marksz, E. , Saremi, S. , McCarter, M. , Reynoso, A. , Long, C. , Hagerstrom, A. , Meyers, D. , Ravi, V. , Prasad, B. , Zhou, H. , Zhang, Z. , Wen, H. , Gomez-Ortiz, F. , Garcia-Fernandez, P. , Bokor, J. , Iniguez, J. , Freeland, J. , Orloff, N. , Junquera, J. , Chen, L. , Salahuddin, S. , , D. , Martin, L. and Ramesh, R. (2020), Local negative permittivity and topological-phase transition in polar skyrmions, Nature Materials, [online], (Accessed September 22, 2021)
Created October 11, 2020, Updated October 15, 2020