Interband optical conductivity of the [001]-oriented Dirac semimetal Cd3As2

We measured the optical reflectivity of [001]-oriented $n$-doped Cd$_{3}$As$_{2}$ in a broad frequency range (50 - 22000 cm$^{-1}$) for temperatures from 10 to 300 K. The optical conductivity, $\sigma(\omega) = \sigma_{1}(\omega) + {\rm i}\sigma_{2}(\omega)$, is isotropic within the (001) plane; its real part follows a power law, $\sigma_{1}(\omega) \propto \omega^{1.65}$, in a large interval from 2000 to 8000 cm$^{-1}$. This behavior is caused by interband transitions between two Dirac bands, which are effectively described by a sublinear dispersion relation, $E(k) \propto \lvert k \rvert ^{0.6}$. The momentum-averaged Fermi velocity of the carriers in these bands is energy dependent and ranges from $1.2 \times 10^{5}$ to $3 \times 10^{5}$ m/s, depending on the distance from the Dirac points. We detect a gaplike feature in $\sigma_{1}(\omega)$ and associate it with the Fermi level positioned around $100$ meV above the Dirac points.