Nontrivial Topology Of Cubic Alkali Bismuthides

We report an ab initio study of the effect of pressure on vibrational and electronic properties of K3Bi and Rb3Bi in the cubic Fm (3) over barm structure. It is shown that the high-temperature cubic phase of K3Bi and Rb3Bi is dynamically unstable at T = 0 but can be stabilized by pressure. The electronic spectra of alkali bismuthides are found to possess the bulk band touching at the Brillouin zone center and an inverted spin-orbit bulk band structure. Upon hydrostatic compression the compounds transform from the topologically nontrivial semimetal (K3Bi)/metal (Rb3Bi) into a trivial semiconductor (metal) with a conical Dirac-type dispersion of electronic bands at the point of the topological transition. In K3Bi the dynamical stabilization occurs before the system undergoes the topological phase transition.