No abstract

Spin-1 chiral semimetal is a new state of quantum matter hosting unconventional chiral fermions that extend beyond the common Dirac and Weyl fermions. B20-type CoSi is a prototypal material that accommodates such an exotic quasiparticle. To date, the spin transport properties in the spin-1 chiral semimetals, have not been explored yet. In this work, we fabricated B20-CoSi thin films on sapphire c-plane substrates by magnetron sputtering and studied the spin Hall effect (SHE) by combining experiments and first-principles calculations. The SHE of CoSi using CoSi/CoFeB/MgO heterostructures was investigated via spin Hall magnetoresistance and harmonic Hall measurements. First-principles calculations yield an intrinsic spin Hall conductivity (SHC) at the Fermi level that is consistent with the experiments and reveal its unique Fermi-energy dependence. Unlike the Dirac and Weyl fermion-mediated Hall conductivities that exhibit a peak-like structure centering around the topological node, SHC of B20-CoSi is odd and crosses zero at the node with two antisymmetric local extrema of opposite sign situated below and above in energy. Hybridization between Co d-Si p orbitals and spin-orbit coupling are essential for the SHC, despite the small (~1%) weight of Si p-orbital near the Fermi level. This work expands the horizon of topological spintronics and highlights the importance of Fermi-level tuning in order to fully exploit the topology of spin-1 chiral fermions for spin current generation.

A density functional theory (DFT)+U method based on linear response (LR) theory was applied to investigate the electronic structures of Co-based full Heusler alloys of ternary Co2YSi and quaternary Co2(Y,Mn)Si.

Dzyaloshinskii-Moriya interaction (DMI) at metallic multilayer interfaces of Co thin films and heavy-metals X (X=Ir, Pt) was investigated from first principles calculations that treat spin-spirals with the spin-orbit coupling. The results predict that the sign of the DMI parameters depends on the heavy-metals at the interfaces, and that the variation of the orbital moments behaves differently depending on the sign of the DMI parameters.