Spin Hall effect in a spin-1 chiral semimetal

TL;DR

This study investigates the spin Hall effect in B20-type CoSi, a spin-1 chiral semimetal hosting unconventional fermions, combining experimental measurements and first-principles calculations to reveal its unique Fermi-energy-dependent spin Hall conductivity.

Contribution

It provides the first experimental and theoretical analysis of spin Hall effect in a spin-1 chiral semimetal, highlighting the role of Fermi-level tuning and orbital hybridization.

Findings

Experimental SHE measurements agree with first-principles calculations.

SHC crosses zero at the topological node, with antisymmetric extrema.

Hybridization and spin-orbit coupling are crucial for SHC.

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.