Comparison of the electronic structures of two non-cuprate layered transition metal oxide superconductors

Comparison is made of the electronic structure of the little-studied layered transition metal oxide LiNbO2 with that of NaxCoO2, which has attracted tremendous interest since superconductivity was discovered in its hydrate. Although the active transition metal d states are quite different due to different crystal fields and band filling, both systems show a strong change of electronic structure with changes in the distance between the transition metal ion layer and the oxygen layers. The niobate is unusual in having a large second-neighbor hopping amplitude, and a nearest-neighbor hopping amplitude that is sensitive to the Nb-O separation. LixNbO2 also presents the attractive simplicity of a single band triangular lattice system with variable carrier concentration that is superconducting.