We report an observation of a pressure-induced breakdown of the three-dimensional Dirac semimetal (3D-DSM) state in $\mathrm{C}{\mathrm{d}}_3\mathrm{A}{\mathrm{s}}_2$, evidenced by a series of in situ high-pressure synchrotron x-ray diffraction and single-crystal transport measurements. We find that $\mathrm{C}{\mathrm{d}}_3\mathrm{A}{\mathrm{s}}_2$ undergoes a structural phase transition from a metallic tetragonal phase in space group $I{4}_1/acd$ to a semiconducting monoclinic phase in space group $P{2}_1/c$ at critical pressure 2.57 GPa; above this pressure, an activation energy gap appears, accompanied by distinct switches in Hall resistivity slope and electron mobility. These changes of crystal symmetry and corresponding transport properties manifest the breakdown of the 3DDSM state in pressurized $\mathrm{C}{\mathrm{d}}_3\mathrm{A}{\mathrm{s}}_2$.

• Received 4 January 2015
• Revised 5 April 2015

DOI:https://doi.org/10.1103/PhysRevB.91.165133