Intertwined Rashba, Dirac and Weyl Fermions in Hexagonal   Hyperferroelectrics
  By means of density functional theory based calculations, we study the role of spin-orbit coupling in the new family of ABC hyperferroelectrics [Phys. Rev. Lett. 112, 127601 (2014)]. We unveil an extremely rich physics strongly linked to ferroelectric properties, ranging from the electric control of bulk Rashba effect to the existence of a three dimensional topological insulator phase, with concomitant topological surface states even in the ultrathin film limit. Moreover, we predict that the topological transition, as induced by alloying, is followed by a Weyl semi-metal phase of finite concentration extension, which is robust against disorder, putting forward hyperferroelectrics as promising candidates for spin-orbitronic applications. 
Domenico Di Sante, Paolo Barone, Alessandro Stroppa, Kevin F. Garrity,   David Vanderbilt, Silvia Picozzi
cond-mat.mtrl-sci