Skyrmion crystal with integer and fractional skyrmion numbers in a nonsymmorphic lattice structure with the screw axis

TL;DR

This study demonstrates the stabilization of skyrmion crystals with integer and fractional skyrmion numbers in a nonsymmorphic lattice with screw symmetry, revealing new phases and mechanisms for skyrmion formation through numerical simulations.

Contribution

It introduces a novel mechanism for skyrmion crystal stabilization in nonsymmorphic lattices without threefold rotational symmetry, using simulated annealing of a layered spin model.

Findings

Skyrmion crystals are stabilized in zero and nonzero magnetic fields.

Two types of layer-dependent skyrmion crystals coexist with spiral states.

A competition between interlayer exchange and anisotropic interactions drives skyrmion formation.

Abstract

The emergence of a magnetic skyrmion crystal in a nonsymmorphic lattice system with the screw symmetry is numerically investigated. By performing the simulated annealing for a layered spin model with the isotropic exchange interaction and the antisymmetric Dzyaloshinskii-Moriya interaction, and then constructing a low-temperature phase diagram, we reveal that the skyrmion crystal is stabilized in both zero and nonzero fields even without the threefold rotational symmetry in the two-dimensional plane. We show that a competition between the ferromagnetic interlayer exchange interaction and the layer- and momentum-dependent anisotropic interactions is a source of the skyrmion crystals in the presence of the screw axis. Moreover, we find two types of layer-dependent skyrmion crystals, which are characterized as a coexisting state of the skyrmion crystal and the spiral state, in the narrow field region. Our result provides a reference for further search of the skyrmion crystals in nonsymmorphic lattice systems.