Comparison of the Electronic Structures of Two Non-cuprate Layered Transition Metal Oxide Superconductors

TL;DR

This paper compares the electronic structures of two layered transition metal oxides, LiNbO₂ and NaₓCoO₂, highlighting how their electronic properties vary with structural changes and their potential for superconductivity.

Contribution

It provides a detailed comparison of the electronic structures of LiNbO₂ and NaₓCoO₂, emphasizing the effects of structural parameters and revealing unique features of LiₓNbO₂ as a single-band triangular lattice superconductor.

Findings

LiNbO₂ has a large second-neighbor hopping amplitude.

Electronic structure varies with transition metal-oxygen layer distance.

LiₓNbO₂ is a simple single-band triangular lattice superconductor.

Abstract

Comparison is made of the electronic structure of the little-studied layered transition metal oxide LiNbO$_2$ with that of Na$_x$CoO$_2$, 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. Li$_x$NbO$_2$ also presents the attractive simplicity of a single band triangular lattice system with variable carrier concentration that is superconducting.