Enhancement of Spin-charge Conversion by Anisotropic Conduction in an Epitaxial Kagome Flatband Metal

In materials with spin-orbit coupling (SOC), spin currents generated by the spin Hall effect can produce spin-orbit torque (SOT), allowing for control over the magnetization of an adjacent ferromagnet. Flatband materials, such as kagome systems, may enhance SOT efficiency due to their unique electronic properties. Flatbands at the Fermi level can lead to anisotropic conductivity, with much lower conductivity in the kagome plane (perpendicular to the c-axis) than along the c-axis. This has been reported in CoSn, which shows an anisotropy ratio of ρ_⊥c : ρ_‖c = 60. [1] In the flatband kagome materials, the spin Hall angle (θ_SH), which quantifies spin-charge conversion efficiency, is expected to scale with this anisotropy ratio. We aim to measure θ_SH in ferromagnet/CoSn heterostructures using quasi-static current-modulated magneto-optic Kerr effect (MOKE) in order to reveal the enhancement of spin-charge conversion. We will also explore SOT in heterostructures of 2D magnets and topological insulators using this technique along with time-resolved MOKE.

[1] H. Huang et al., Flat-Band-Induced Anomalous Anisotropic Charge Transport and Orbital Magnetism in Kagome Metal CoSn, Phys. Rev. Lett. 128, 096601 (2022).