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3D Topological Solitons in Colloidal Chiral Ferromagnets - Ivan I. Smalyukh

06/06/2017 - Salle S208

3D topological solitons are continuous but topologically nontrivial field configurations localized in 3D-space and embedded in a uniform far-field background, that behave like particles and cannot be transformed to a uniform state through smooth deformations. Many topologically nontrivial 3D-solitonic fields have been proposed. Yet, according to the Hobart-Derrick theorem, physical systems cannot host them, except for nonlinear theories with higher-order derivatives such as the Skyrme-Faddeev model. Experimental discovery of such solitons is hindered by the need of spatial imaging of the 3D fields. I will discuss how we experimentally realize and numerically model stationary topological solitons in a chiral ferromagnet formed by colloidal dispersions of magnetic nanoplates [1,2]. Such solitons have closed-loop preimages, 3D regions with a single orientation of the magnetization field. I will discuss localized solitonic structures with different linking of preimages quantified by topological Hopf invariants [2]. I will show that the hosting medium’s chirality helps overcoming the constraints of the Hobart-Derrick theorem, like in two-dimensional solid-state ferromagnetic solitons called “Skyrmions”. Finally, I will discuss how these findings may lead to the observation of 3D topological solitons with nonzero Hopf indices in solid-state ferromagnets and also to many technological applications.

1. Q. Liu, P.J. Ackerman, T. C. Lubensky and I. I. Smalyukh. “Biaxial ferromagnetic liquid crystal colloids.” Proc. Natl. Acad. Sci. U.S.A. 113, 10479–10484 (2016).

2. A. Mertelj, D. Lisjak, M. Drofenik, & M. Čopič. “Ferromagnetism in suspensions of magnetic platelets in liquid crystal.” Nature 504, 237–241 (2013).

3. P. J. Ackerman and I. I. Smalyukh. “Static 3D knotted solitons in fluid chiral ferromagnets and colloids.” Nature Mater 16, 426-432 (2017).