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.
Categories: cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.str-el