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Experimental verification of the rotational sense and type of chiral spin spiral structure by spin-polarized scanning tunneling microscopy

We report on experimental verification of the rotational sense and type of homogeneous chiral spin spiral order in a Mn monolayer on a W(110) substrate using spin-polarized scanning tunneling microscopy. We found that the magnetic contrast due to the spin spiral order almost vanishes with a magnetic tip magnetized normal to the (001) plane, indicating that the spin spiral rotates in the plane. From a shift in the most-contrasted sites by changing the tip magnetization direction within the rotating plane, we reveal that the rotational sense is left-handed, consistent with the previous results predicted by first-principle calculations. By comparing the current system with a chiral magnetic domain wall in Fe double layers on the same substrate, we found that the polarity of the Dzyaloshinskii--Moriya interaction, the driving force of those chiral magnets, is dominantly determined by the choice of the substrate rather than the overlayer.