Search for topological insulators in the family of oxides

Topological insulators (TIs) (like Bi₂Se₃, Bi₂Te₃, and TlBiSe₂) usually suffer from heavy defect doping and surface degradation, hindering the achievement of transport measurements and device applications. From the viewpoint of stable compounds against degradation and oxidization, oxides are ideal choices of TIs. Because the eg-t2g bands of the perovskite structure (ABO₃) have the same parities of "+", we must go beyond simple pervoskites and look for complex structures. Therein eg-t2g orbitals can reorganize to form states of different parities. Many oxides crystalize in the perovskite structure, the honeycomb lattice, the pyrochlore lattice or spinel structure. The first candidates under investigation will be the honecomb compound Ag₅Pb₂O₇, and its variations, Ag₅HgSbO₇, Ag₅PbBiO₇, Ag₄P_2-xBi_xO₅ etc. First-principles calculations with LDA+U and even GW methods will be employed to investigate the band structures as TI candidates. Identified oxides will be synthesized via various solid state methods. Later we will search for topological oxides with highly correlated electrons such as 5d and 4f or 5f electrons.