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

Abstract

Recently discovered a family of Weyl semimetals, LaAlX (X=Si, Ge), show coexistence of multiple types of nodal lines and points near the Fermi level (E F ), which may possess large intrinsic spin Hall effect (SHE) and high conversion efficiency of charge-to-spin current by the spin-orbit torque. Here, we theoretically study the intrinsic spin Hall conductivity (SHC) and electrical conductivity in nonmagnetic LaAlSi and LaAlGe by the first-principles calculations. Our results show that both of them exhibit large intrinsic SHC, varying from -210 to -361 ( /e) S/cm, which can be further boosted to -560 ( /e) S/cm by 0.01 hole doping/uc. The calculated spin Hall angle of LaAlSi and LaAlGe is 0.040 and 0.046 respectively, which is comparable to Pt, showing a high efficient charge-spin current conversion in LaAlX. The underlying physics of such high SHC and its enhancement by h-doping is revealed by the band-resolved and k-resolved spin Berry curvature.The strong SHE in LaAlX originates from the multiple slightly anticrossings of nodal lines and points near E F due to their high mirror symmetry and large spin-orbit coupling.