Hybridization and anisotropy in the exchange interaction in 3D Dirac semimetals

N. SANDLER; MASTROGIUSEPPE, D.; ULLOA, SERGIO E.

Beijing

Conferencia; ICPS 2016; 2016

Dirac semimetals are fascinating new materials that can be considered analogues of graphene in three dimensions. They possess robust Dirac points that are protected by crystalline symmetry, and strong spin-orbit interaction. Na3Bi (Fig. 1, left and center panels) and Cd3As2 are among the most studied compounds. We study the Ruderman-Kittel-Kasuya-Yosida interaction between magnetic impurities in these materials. Using retarded Green's functions in real space, we obtain and analyze asymptotic expressions for the interaction, with impurities at different distances and relative angle with respect to high symmetry directions on the lattice. In general, we find that the effective impurity interaction has three competing components: Heisenberg, Ising, and Dzyaloshinskii-Moriya (DM). There are three important factors that come into play for the resultant interaction. First, the Fermi velocity anisotropy modifies the period of the oscillation as a function of the impurity separation, and enhances its magnitude (Fig. 1, right panel). Second, the position of the Dirac points in the Brillouin zone, results in a second modulation along the z direction. Lastly, the orbitals to which the impurities hybridize have impact on the angular dependence of the interaction in the xy plane. When both impurities couple to the same type of orbital (Na-S or Bi-P), the interaction is angular-independent, and the DM component vanishes due to symmetry considerations. When impurities hybridize to a different orbitals, there is a strong modulation with the orientation in the lattice. The different components of the interaction survive depending on the directions along the crystal, resulting in complex equilibrium configurations for an impurity ensemble, which could be tested by NMR and µSR experiments.