Locking of skyrmion cores on a centrosymmetric discrete lattice: onsite versus offsite

TL;DR

This paper investigates the positional locking of skyrmion cores on a discrete lattice, revealing conditions under which they are locked at interstitial or onsite positions, and discusses implications for Fermi surface topology and experimental detection.

Contribution

It provides a theoretical analysis of skyrmion core positions on a discrete lattice, highlighting the effects of anisotropy and symmetry on core locking and electronic structure.

Findings

Skyrmion cores are locked at interstitial sites without anisotropy.

Large easy-axis anisotropy shifts cores to onsite positions.

Different core positions lead to distinguishable Fermi surface topologies.

Abstract

A magnetic skyrmion crystal (SkX) with a swirling spin configuration, which is one of topological spin crystals as a consequence of an interference between multiple spin density waves, shows a variety of noncoplanar spin patterns depending on a way of superposing the waves. By focusing on a phase degree of freedom among the constituent waves in the SkX, we theoretically investigate a position of the skyrmion core on a discrete lattice, which is relevant with the symmetry of the SkX. The results are obtained for the double exchange (classical Kondo lattice) model on a discrete triangular lattice by the variational calculations. We find that the skyrmion cores in both two SkXs with the skyrmion number of one and two are locked at the interstitial site on the triangular lattice, while it is located at the onsite by introducing a relatively large easy-axis single-ion anisotropy. The variational parameters and the resultant Fermi surfaces in each SkX spin texture are also discussed. The different symmetry of the Fermi surfaces depending on the core position is obtained when the skyrmion crystal is commensurate with the lattice. The different Fermi-surface topology is directly distinguished by an electric probe of angle-resolved photoemission spectroscopy. Furthermore, we show that the SkXs obtained by the variational calculations are also confirmed by numerical simulations on the basis of the kernel polynomial method and the Langevin dynamics for the double exchange model and the simulated annealing for an effective spin model.