Spectroscopic evidence of topological phase transition in the three-dimensional Dirac semimetal Cd_3(As_(1-x)P_x)_2

摘要

We study the low-energy electronic structure of three-dimensional Dirac semimetal, Cd_3(As_(1-x)P_x)_2 [x = O and 0.34(3)], by employing angle-resolved photoemission spectroscopy (ARPES). We observe that the bulk Dirac states in Cd_3(As_(0.66)P_(0.34))_2 are gapped out with an energy of 0.23 eV, contrary to the parent Cd_3As_2 in which the gapless Dirac states have been observed. Thus, our results confirm the earlier predicted topological phase transition in Cd_3As_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 Cd_3As_2 form a single Dirac point at Γ, is much lower [x_c(P) < 0.34(3)] than the predicted value of x_c(P) = 0.9. Therefore, our results suggest that the nontrivial band topology of Cd_3As_2 is remarkably sensitive to the P substitution and can only survive over a narrow substitution range, i.e., 0 ≤ x(P) < 0.34(3).