Impurity-induced topological phase transitions in Cd3As2 and Na3Bi Dirac semimetals

Using first-principles density functional theory calculations, combined with a topological analysis, we have investigated the electronic properties of Cd3As2 and Na3Bi Dirac topological semimetals doped with nonmagnetic and magnetic impurities. Our systematic analysis shows that the selective breaking of the inversion, rotational, and time-reversal symmetry, controlled by specific choices of the impurity doping, induces phase transitions from the original Dirac semimetal to a variety of topological phases such as topological insulator, trivial semimetal, nonmagnetic and magnetic Weyl semimetal, and Chern insulator. The Dirac semimetal phase can exist only if the rotational symmetry C-n with n > 2 is maintained. One particularly interesting phase emerging in doped Cd3As2 is a coexisting Dirac-Weyl phase, which occurs when only inversion symmetry is broken while time-reversal symmetry and rotational symmetry are both preserved. To further characterize the low-energy excitations of this phase, we have complemented our density functional results with a continuum four-band k . p model, which indeed displays nodal points of both Dirac and Weyl types. The coexisting phase appears as a transition point between two topologically distinct Dirac phases but may also survive in a small region of parameter space controlled by external strain.