Giant spin Hall effect in two-dimensional monochalcogenides*

One of the most exciting properties of two dimensional materials is their sensitivity to external tuning of the electronic properties, for example via electric field or strain. Recently discovered analogues of phosphorene, group-IV monochalcogenides (MX with M = Ge, Sn and X = S, Se, Te), display several interesting phenomena related to the in-plane strain, such as giant piezoelectricity and multiferroicity, which combines ferroelastic and ferroelectric properties. Here, using calculations from first principles, we predict for the first time giant spin Hall effect (SHE) in these materials which suggests their high potential for 2D spintronics. We reveal that the spin Hall conductivity is tunable via combinations of external strain and doping. In some configurations, the strain-induced semiconductor to metal transition enables the logic functionality of switch on/off control of spin currents indicating a new route for the design of multi-tunable spintronics devices.