Origin and Large Enhancement of Large Spin Hall Angle in Weyl Semimetals LaAl$X$ ($X$=Si, Ge)

Abstract

We study the origin of the strong spin Hall effect (SHE) in a recently discovered family of Weyl semimetals, LaAl$X$ ($X$=Si, Ge) via a first-principles approach with maximally localized Wannier functions. We show that the strong intrinsic SHE in LaAl$X$ originates from the multiple slight anticrossings of nodal lines and points near $E_F$ due to their high mirror symmetry and large spin-orbit interaction. It is further found that both electrical and thermal means can enhance the spin Hall conductivity (${\sigma }_{SH}$). However, the former also increases the electrical conductivity (${\sigma }_c$), while the latter decreases it. As a result, the independent tuning of ${\sigma }_{SH}$ and ${\sigma }_c$ by thermal means can enhance the spin Hall angle (proportional to $\frac{{\sigma }_{SH}}{{\sigma }_c}$), a figure of merit of charge-to-spin current interconversion of spin-orbit torque devices. The underlying physics of such independent changes of the spin Hall and electrical conductivity by thermal means is revealed through the band-resolved and $k$-resolved spin Berry curvature. Our finding offers a new way in the search of high SHA materials for room-temperature spin-orbitronics applications.

21 pages, 6 figures

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