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arXiv · 2204.08614

Higher-order modulations in the skyrmion-lattice phase of Cu$_2$OSeO$_3$

Johannes D. Reim·Shinnosuke Matsuzaka·Koya Makino·Seno Aji·Ryo Murasaki·Daiki Higashi·Daisuke Okuyama·Yusuke Nambu·Elliot P. Gilbert·Norman Booth·Shinichiro Seki·Yoshinori Tokura·Taku J Sato
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Abstract

Using small angle neutron scattering, we have investigated higher-order peaks in the skyrmion-lattice phase of Cu$_2$OSeO$_3$, in which two different skyrmion lattices, SkX1 and SkX2, are known to form. For each skyrmion-lattice phase, we observed two sets of symmetrically inequivalent peaks at the higher-order-reflection positions with the indices $(110)$ and $(200)$. Under the condition where the SkX1 and SkX2 coexist, we confirmed the absence of the scattering at $\mathbf{Q}$ positions combining reflections from the two phases, indicating a significantly weak double-scattering component. Detailed analysis of the peak profile, as well as the temperature and magnetic-field dependence of the peak intensity, also supports the intrinsic higher-order modulation rather than the parasitic double scattering. The two higher-order modulations show contrasting magnetic-field dependence; the former $(110)$ increases as the field is increased, whereas the latter $(200)$ decreases. This indicates that, in Cu$_2$OSeO$_3$, skyrmions are weakly distorted, and the distortion is field-dependent in a way that the dominant higher-order modulation switches from $(110)$ to $(200)$ under field. Monte Carlo simulations under sweeping external magnetic field qualitatively reproduce the observed magnetic-field dependence, and suggests that the higher-order modulations correspond to the superlattices of weak swirlings appearing in the middle of the original triangular-latticed skyrmions.

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Johannes D. Reim, Shinnosuke Matsuzaka, Koya Makino, Seno Aji, Ryo Murasaki, Daiki Higashi, Daisuke Okuyama, Yusuke Nambu, Elliot P. Gilbert, Norman Booth, Shinichiro Seki, Yoshinori Tokura, Taku J Sato. 2022-04-19. Higher-order modulations in the skyrmion-lattice phase of Cu$_2$OSeO$_3$. https://doi.org/10.1103/physrevb.106.104406

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