We study the low-energy electronic structure of three-dimensional Dirac semimetal, ${\mathrm{Cd}}_3{\left({\mathrm{As}}_{1-x}{\mathrm{P}}_x\right)}_2$ [$x=0$ and 0.34(3)], by employing angle-resolved photoemission spectroscopy (ARPES). We observe that the bulk Dirac states in ${\mathrm{Cd}}_3{\left({\mathrm{As}}_{0.66}{\mathrm{P}}_{0.34}\right)}_2$ are gapped out with an energy of 0.23 eV, contrary to the parent ${\mathrm{Cd}}_3{\mathrm{As}}_2$ in which the gapless Dirac states have been observed. Thus, our results confirm the earlier predicted topological phase transition in ${\mathrm{Cd}}_3{\mathrm{As}}_2$ with perturbation. We further notice that the critical P substitution concentration, at which the two Dirac points that are spread along the $c$-axis in ${\mathrm{Cd}}_3{\mathrm{As}}_2$ form a single Dirac point at $\mathrm{<ruby><rb>\Gamma </rb><rt>がんま</rt></ruby>}$, is much lower [$x_c\left(\mathrm{P}\right)<0.34\left(3\right)$] than the predicted value of $x_c\left(\mathrm{P}\right)=0.9.$ Therefore, our results suggest that the nontrivial band topology of ${\mathrm{Cd}}_3{\mathrm{As}}_2$ is remarkably sensitive to the P substitution and can only survive over a narrow substitution range, i.e., $0\le x\left(\text{P}\right)<0.34\left(3\right)$.

• Received 12 February 2018

DOI:https://doi.org/10.1103/PhysRevB.98.085145