How to reveal metastable skyrmionic spin structures by spin-polarized scanning tunneling microscopy

<p>We predict the occurrence of metastable skyrmionic spin structures such as antiskyrmions and<br> higher-order skyrmions in ultra-thin transition-metal films at surfaces using Monte Carlo simulations<br> based on a spin Hamiltonian parametrized from density functional theory calculations.Weshow that<br> such spin structures will appear with a similar contrast in spin-polarized scanning tunneling<br> microscopy images. Both skyrmions and antiskyrmions display a circular shape for out-of-plane<br> magnetized tips and a two-lobe butterfly contrast for in-plane tips. An unambiguous distinction can<br> be achieved by rotating the tip magnetization direction without requiring the information of all<br> components of the magnetization.</p>