Determination of the crystal field splitting energy in Cd3As2 using magnetooptics

Symmetry considerations are of extreme importance to the topological properties of crystals. A crystal field splitting $\ensuremath{\delta}$ yields Dirac nodes near the Brillouin zone center in $\mathrm{C}{\mathrm{d}}₃\mathrm{A}{\mathrm{s}}₂$, but its value has yet to be determined with precision. We study the band structure of $\mathrm{C}{\mathrm{d}}₃\mathrm{A}{\mathrm{s}}₂$ using magnetooptical infrared spectroscopy measurements on epilayers with low carrier density grown by molecular beam epitaxy. By combining angular dependent cyclotron resonance with Landau level spectroscopy measurements in the Faraday geometry, we determine that $\ensuremath{\delta}$ is positive and equal to $15\ifmmode\pm\else\textpm\fi{}5$ meV in $\mathrm{C}{\mathrm{d}}₃\mathrm{A}{\mathrm{s}}₂$. Our results lead to a more accurate knowledge of the details of the band structure of this Dirac semimetal such as the position its Dirac nodes in momentum space and their splitting into Weyl nodes under a magnetic field.