Crystal size effects on giant thermopower in CrSb2

We have examined size effect on thermal, transport, and thermodynamic properties of a ${\mathrm{CrSb}}_{2}$ single crystal. We demonstrate highly anisotropic quasi-one-dimensional electrical conductivity, quasiballistic phonons, and giant thermopower of $\ensuremath{-}6$ mV/K at 15 K. A thermopower peak is suppressed to $\ensuremath{-}1.6$ mV/K by changing crystal dimensions and shows linear dependence on the phonon mean-free path. Whereas electronic diffusion thermopower is significant, the bulk of the giant thermopower in ${\mathrm{CrSb}}_{2}$ stems from the coupling of the very long mean-free path phonons with the in-gap states.