Shifting of Fermi Level and Realization of Topological Insulating Phase in the Oxyfluoride BaBiO\(_2\)F

The disadvantage of BaBiO\(_3\) of not being a topological insulator despite having symmetry protected Dirac state is overcome by shifting the Fermi level (E\(_F\)) 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 E\(_F\). We find that 33 % fluorination is sufficient to shift the E\(_F\) by \(\sim\) 2 eV so that the invariant Dirac state lies on it to make BaBiO\(_2\)F a topological insulator. The fluorinated cubic compound can be experimentally synthesized as the phonon studies predict dynamical stability above \(\sim\) 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, ABiO\(_3\) (A = Na, K, Cs, Ba, Sr, Ca), to real topological insulator through appropriate fluorination.