Kagome and Van der Waals Magnetic Topological Materials

Materials and heterostructures combining magnetic order and band topology are important for science and technology ranging from quantum anomalous Hall effect (QAHE) to highly efficient spin-orbit torque switching. Kagome lattice metals and van der Waals (vdW) heterostructures are two classes of materials that are particularly promising in this regard. The 2D kagome lattice has topological flat bands and Dirac cones inherent in its band structure and these features persist in compounds with layered kagome lattices. Meanwhile, vdW materials encompass 2D magnets and topological insulators that manifest the QAHE, most notably Cr-doped (Bi,Sb)₂Te₃ and MnBi₂Te₄. Our research has focused on the atomic layer-by-layer synthesis of kagome and vdW materials by molecular beam epitaxy and their characterization through magneto-optics, angle-resolved photoemission spectroscopy (ARPES), and magnetotransport. For kagome metals, we investigated spin-orbit torque effects in Fe₃Sn₂ by magneto-optic methods [1,2] and flat bands in CoSn by ARPES [3]. Recently, we demonstrated the first thin film growth of rare-earth kagome magnets (RMn₆Sn₆, R = rare-earth Tb, Er), which are prospective QAHE materials. For vdW materials, we developed thin films of layered antiferromagnetic topological insulator MnBi₂Se₄ [4], which cannot be stabilized in bulk vdW crystal form, and Fe₃GeTe₂/Bi₂Te₃ heterostructures. The latter are heterostructures combining topological insulators and 2D magnets, where the Curie temperature has been raised to above room temperature by varying growth conditions [5].<br/><br/>[1] Shuyu Cheng et al., APL Materials 10, 061112 (2022).<br/>[2] Igor Lyalin et al., Nano Letters 21, 6975 (2021).<br/>[3] Shuyu Cheng et al., Nano Letters 23, 7107 (2023).<br/>[4] Tiancong Zhu et al., Nano Letters 21, 5083 (2021).<br/>[5] Wenyi Zhou et al., arXiv:2308.13620 (accepted to Physical Review Materials)