Broken of translational symmetry plays a vital role in the stabilization of three-dimensional magnetic skyrmions. The absence of exchange neighbours at truncated surfaces leads to surface twist effect, resulting in twisted helicity angle of the skyrmions. Recently, it was reported in Zhang et al. [Proc. Natl. Acad. Sci. USA 115, 6386 (2018)] that the observed surface twist effect is over an order of magnitude more pronounced than the theoretical predictions. Nevertheless, the underlying mechanism that leads to such discrepancy has not been resolved yet. In order to address this long-standing issue, we performed depth-resolved circular dichroic resonant elastic x-ray scattering (CD-REXS) measurements on the skyrmion lattice phase in ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$ over a wide temperature range. It is found that the measured skyrmion helicity angle profile is highly temperature-dependent, which cannot be quantitatively explained by the temperature-varying micromagnetic parameters alone. By systematically ruling out other possible effects, we conclude that a giant surface-type Dzyaloshinskii-Moriya interaction emerges due to the ferroelectric polarization at the surface of ${\mathrm{Cu}}_2{\mathrm{OSeO}}_3$. Our results provide insights into the complex interplay between surface and bulk interactions in the formation of magnetic skyrmions and offer new possibilities for designing skyrmionic devices.

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• Magnetic interactions
• Micromagnetism
• Skyrmions
• Topological materials