Topological Hall effect in a system with magnetic skyrmions

LTL Quantum Physics Seminar (Nanotalo). Speaker: Dr. Igor Rozhansky (Ioffe Institute, Russia).

Topological Hall effect (THE) is a recently discovered transport phenomenon occurring in various magnetic systems due to free carriers exchange interaction with chiral magnetization textures, such as magnetic skyrmions. THE is considered as a perspective tool to probe topologically nontrivial spin structures as well as for potential device applications such as racetrack memory.

Despite its great importance, THE has still lacked a proper theoretical description. The existing theories considered two limiting cases of either infinitely strong exchange interaction when the geometric Berry phase approach is applicable or the case of a weak exchange interaction allowing for perturbation theory analysis. These two approaches give qualitatively different results. The Berry phase approximation has revealed that THE is accompanied with a transverse spin current so the appearance of charge Hall current requires spin polarization of the carriers. In the opposite case of a weak exchange the transverse charge current occurs in the absence of a spin current and THE is expected even for non-polarized carriers.

We have developed a theory of THE based on exact solution of a problem of electron scattering on a chiral spin field. We show how the transverse charge current in the weak coupling case transforms into a transverse spin current in the adiabatic regime. Another interesting finding is that unlike previously thought the topological charge of a magnetic skyrmion is not crucial for THE. Chiral magnetic vortices exhibit THE similar to that in magnetic skyrmions.