Existence of higher degree minimizers in the magnetic skyrmion problem

Muratov, C.B.; Simon, T.M.; Slastikov, V.V.

Abstract

We demonstrate existence of topologically nontrivial energy minimizing maps of a given positive degree from bounded domains in the plane to 𝕊^2 in a variational model describing magnetizations in ultrathin ferromagnetic films with Dzyaloshinskii-Moriya interaction. Our strategy is to insert tiny truncated Belavin-Polyakov profiles in carefully chosen locations of lower degree objects such that the total energy increase lies strictly below the expected Dirichlet energy contribution, ruling out loss of degree in the limits of minimizing sequences. The argument requires that the domain be either sufficiently large or sufficiently slender to accommodate a prescribed degree. We also show that these higher degree minimizers concentrate on point-like skyrmionic configurations in a suitable parameter regime.