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

We study the origin of the strong spin Hall effect (SHE) in a recently discovered family of Weyl semimetals, LaAlX (X=Si, Ge) via a first-principles approach with maximally localized Wannier functions. We show that the strong intrinsic SHE in LaAlX originates from the multiple slight anticrossings of nodal lines and points near EF due to their high mirror symmetry and large spinorbit interaction. It is further found that both electrical and thermal means can enhance the spin Hall conductivity (σSH). However, the former also increases the electrical conductivity (σc), while the latter decreases it. As a result, the independent tuning of σSH and σc by thermal means can enhance the spin Hall angle (proportional to σSH σc ), 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.