Square skyrmion lattice in multiorbital $f$-electron systems

TL;DR

This paper predicts the formation of a square skyrmion lattice in multi-orbital $f$-electron systems with easy-axis anisotropy, using mean-field calculations to explore phase diagrams and identify novel magnetic states.

Contribution

It introduces a new theoretical prediction of square skyrmion lattices in centrosymmetric $f$-electron systems with multi-orbital degrees of freedom, expanding potential material candidates.

Findings

Square skyrmion lattice appears in intermediate magnetic fields.

A double-$Q$ state with nonzero scalar chirality exists at low fields.

The results suggest new materials, like Ce-based compounds, for skyrmion hosting.

Abstract

We report the emergence of a square-shaped skyrmion lattice in multi-orbital $f$-electron systems with easy-axis magnetic anisotropy on a centrosymmetric square lattice. By performing mean-field calculations for an effective localized model consisting of two Kramers doublets, we construct the low-temperature phase diagram in a static external magnetic field. Consequently, we find that a square-shaped skyrmion lattice with the skyrmion number of one appears in the intermediate-field region when the crystal field splitting between the two doublets is small. Furthermore, we identify another double-$Q$ state with a nonzero net scalar chirality at zero- and low-field regions, which is attributed to the help of the multi-orbital degree of freedom. Our results offer another route to search for skyrmion-hosting materials in centrosymmetric $f$-electron tetragonal systems with multi-orbital degrees of freedom, e.g., Ce-based compounds. This contrasts with conventional other $f$-electron systems hosting skyrmion lattices, such as Gd- and Eu-based compounds without orbital angular momentum.