Spin Hall effect in a spin-1 chiral semimetal

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.

Helicity-tunable spin Hall and spin Nernst effects in unconventional chiral fermion semimetals XY (X=Co, Rh; Y=Si, Ge)

“…In the past few years, the study of SHE [19][20][21][22][23][24][25][26][27][28] and SNE [22,26] in so-called topological semimetals has attracted considerable attention. In high-energy physics, the standard model predicts three kinds of fermionic particles in the Universe, namely, Dirac, Weyl and Majorana fermions, on the basis of the Poincare group.…”

“…Among the CoSi family, only the SHE in CoSi was recently studied by combining experiments and firstprinciples calculations, and the SHC (σ z xy ) was found to be quite large. [28] However, the other SHC element σ y xz was not considered in Ref. [28].…”

“…[28] However, the other SHC element σ y xz was not considered in Ref. [28]. As will be reported below in Sec.…”

“…Thus, one could expect the CoSi family to be exploited for thermal spin current generation via SNE. Furthermore, recent first-principles calculations [28] showed that the energy derivative of the SHC σ z xy (E F ) ′ at the Fermi level (E F ) in CoSi is very large. This further suggests that large SNE could occur in the CoSi family because the Mott relation [see Eq.…”

Giant Fully Spin-Polarized Currents Enhanced by Disorder in Nodal Chain Spin-Gapless Semimetals

“…On the other hand, the Hall currents of spin J S H − i.e. the spin counterparts of J A H also known as the spin Hall effect (SHE) [48] and spin Nernst effect (SNE) [49] − are also largely driven by topological nodal features which give rise to large spin Hall conductivity (SHC) and spin Nernst conductivity (SNC) in non-magnetic topological semimetals [50][51][52][53][54][55][56][57][58][59][60][61][62][63].…”