Are topological Hall signals in thin films evidence of skyrmions?
In plain words
Skyrmions should deflect electrons and add a bump to the Hall voltage, called the topological Hall effect. Many reported bumps in thin films can also come from two magnetic layers or regions with opposite ordinary anomalous Hall signals, so they may not prove skyrmions exist.
Precise statement
For films and heterostructures (SrRuO3-based, Mn-based, magnetic topological insulators) with reported humps in $\rho_{xy}(H)$, determine for each whether the hump follows $\rho_{TH} \sim P R_0 n_{sk} \Phi_0$ ($P$ spin polarization, $R_0$ ordinary Hall coefficient, $n_{sk}$ skyrmion density, $\Phi_0$ flux quantum) or arises from superposed anomalous Hall loops of opposite sign. An answer is a criterion that separates the two and its application with direct imaging of $n_{sk}$.
What would settle it
Simultaneous Hall transport and real-space magnetic imaging (Lorentz electron microscopy, magnetic force microscopy or NV magnetometry) on the same device across the field range of the hump.