Giant and robust intrinsic spin Hall effects in metal dihydrides: A first-principles prediction

Topological nodal line semimetals offer an attractive platform to investigate exotic phenomena related to spintronics. Herein, we discover the existence of topological nodal-net semimetal states in metal dihydrides $M{\mathrm{H}}_{2}$ ($M=\mathrm{Hf}$, Th), a class of well-known hydrogen storing and superconducting materials. These materials host a fascinating nodal-net-like band degeneracy around the Fermi level, including triply degenerate points and multiple Dirac nodal lines (DNLs) in three mirror planes. Importantly, the inclusion of spin-orbit coupling breaks the degeneracy of DNLs, contributing to giant spin Hall conductivity values that are robust against large concentrations of charge doping. Furthermore, due to the rather small intrinsic electronic conductivities, large spin Hall angles can be achieved in $M{\mathrm{H}}_{2}$ for practice applications.