Ab initio probing of the electronic band structure and Fermi surface of fluorine-doped WO3 as a novel low-TC superconductor

摘要

First-principles calculations were performed to investigate the electronicstructure and the Fermi surface of the newly discovered low-temperaturesuperconductor: fluorine-doped WO3. We find that F doping provides thetransition of the insulating tungsten trioxide into a metallic-like phaseWO3-xFx, where the near-Fermi states are formed mainly from W 5d with admixtureof O 2p orbitals. The cooperative effect of fluorine additives in WO3 consistsin change of electronic concentration as well as the lattice constant. Atprobing their influence on the near-Fermi states separately, the dominant roleof the electronic factor for the transition of tungsten oxyfluoride intosuperconducting state was established. The volume of the Fermi surfacegradually increases with the increase of the doping. In the sequence WO3\rightarrow WO2.5F0.5 the effective atomic charges of W and O ions decrease,but much less, than it is predicted within the idealized ionic model - owing topresence of the covalent interactions W-O and W-F.