Shifting of Fermi level and realization of topological insulating phase in the oxyfluoride BaBiO<inf>2</inf>F

The disadvantage of BaBiO3 of not being a topological insulator despite having symmetry protected Dirac state is overcome by shifting the Fermi level (EF) via fluorination. The DFT calculations reveal that the fluorination neither affects the spin-orbit coupling nor the parity of the states, but it acts as a perfect electron donor to shift the EF. We find that 33% fluorination is sufficient to shift the EF by ∼2 eV so that the invariant Dirac state lies on it to make BaBiO2F a topological insulator. The fluorinated cubic compound can be experimentally synthesized as the phonon studies predict dynamical stability above ∼500 K. Furthermore, the Dirac states are found to be invariant against the low-temperature phase lattice distortion which makes the structure monoclinic. The results carry practical significance as they open up the possibility of converting the family of superconducting oxides, ABiO3 (A = Na, K, Cs, Ba, Sr, Ca), to real topological insulator through appropriate fluorination.