Magnetism and spin–orbit coupling are two quintessential ingredients underlying topological transport phenomena in itinerant ferromagnets. When spin-polarized bands support nodal points/lines with band degeneracy that can be lifted by spin–orbit coupling, the nodal structures become a source of Berry curvature, leading to a large anomalous Hall effect. However, two-dimensional systems can possess stable nodal structures only when proper crystalline symmetry exists. Here we show that two-dimensional spin-polarized band structures of perovskite oxides generally support symmetry-protected nodal lines and points that govern both the sign and the magnitude of the anomalous Hall effect. To demonstrate this, we performed angle-resolved photoemission studies of ultrathin films of SrRuO3, a representative metallic ferromagnet with spin–orbit coupling. We show that the sign-changing anomalous Hall effect upon variation in the film thickness, magnetization and chemical potential can be well explained by theoretical models. Our work may facilitate new switchable devices based on ferromagnetic ultrathin films.
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The data that support the findings of this study are available from the corresponding authors on request.
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We gratefully acknowledge discussions with J. R. Kim. This work is supported by IBS-R009-D1 and IBS-R009-G2 through the Institute for Basic Science (IBS) Center for Correlated Electron Systems. B.-J.Y. was supported by the Institute for Basic Science in Korea (grant no. IBS-R009-D1), Samsung Science and Technology Foundation under project no. SSTF-BA2002-06, the National Research Foundation of Korea (NRF) Grant funded by the Korea government (MSIT) (no. 2021R1A2C4002773, and no. NRF-2021R1A5A1032996), and the US Army Research Office and Asian Office of Aerospace Research & Development (AOARD) under grant no. W911NF-18-1-0137. S.Y.P. was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (no. 2021R1C1C1009494) and by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (no. 2021R1A6A1A03043957). The Advanced Light Source is supported by the Office of Basic Energy Sciences of the US Department of Energy under contract no. DE-AC02-05CH11231.
The authors declare no competing interests.
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Sohn, B., Lee, E., Park, S.Y. et al. Sign-tunable anomalous Hall effect induced by two-dimensional symmetry-protected nodal structures in ferromagnetic perovskite thin films. Nat. Mater. (2021). https://doi.org/10.1038/s41563-021-01101-4