  We report measurements demonstrating that when the Neel vector of the
collinear antiferromagnet RuO2 is appropriately canted relative to the sample
plane, the antiferromagnet generates a substantial out of plane damping-like
torque. The measurements are in good accord with predictions that when an
electric field, E is applied to the spin split band structure of RuO2 it can
cause a strong transverse spin current even in the absence of spin-orbit
coupling. This produces characteristic changes in all three components of the E
induced torque vector as a function of the angle of E relative to the crystal
axes, corresponding to a spin current with a well defined tilted spin
orientation s approximately (but not exactly) parallel to the Neel vector,
flowing perpendicular to both E and S. This angular dependence is the signature
of an antiferromagnetic spin Hall effect with symmetries that are distinct from
other mechanisms of spin-current generation reported in antiferromagnetic or
ferromagnetic materials.
