  We report giant thermopower S = 2.5 mV/K in CoSbS single crystals, a material
that shows strong high-temperature thermoelectric performance when doped with
Ni or Se. Changes of low temperature thermopower induced by magnetic field
point to mechanism of electronic diffusion of carriers in the heavy valence
band. Intrinsic magnetic susceptibility is consistent with the Kondo-
Insulator-like accumulation of electronic states around the gap edges. This
suggests that giant thermopower stems from temperature-dependent
renormalization of the non-interacting bands and buildup of the electronic
correlations on cooling.
