  Carrier dynamics acquire a new character in the presence of Bloch-band Berry
curvature, which naturally arises in gapped Dirac materials (GDMs). Here we
argue that photoresponse in GDMs with small band gaps is dramatically enhanced
by Berry curvature. This manifests in a giant and saturable Hall
photoconductivity when illuminated by circularly polarized light. Unlike Hall
motion arising from a Lorentz force in a magnetic field, which impedes
longitudinal carrier motion, Hall photoconductivity arising from Berry
curvature can boost longitudinal carrier transport. In GDMs, this results in a
helicity-dependent photoresponse in the Hall regime, where photoconductivity is
dominated by its Hall component. We find that the induced Hall conductivity per
incident irradiance is enhanced by up to six orders of magnitude when moving
from the visible regime (with corresponding band gaps) to the far infrared.
These results suggest that narrow-gap GDMs are an ideal test-bed for the unique
physics that arise in the presence of Berry curvature, and open a new avenue
for infrared and terahertz optoelectronics.
