Electronic Structure of Sodium Cobalt Oxide: Comparing Mono- and Bilayer-hydrate

TL;DR

This study uses density functional calculations to compare the electronic structures of superconducting sodium cobalt oxide bilayer-hydrate and non-superconducting monolayer hydrate, revealing key differences in their band dispersions.

Contribution

It provides a detailed comparison of the electronic structures of BLH and MLH, highlighting the role of the $a_{1g}$ band dispersion in superconductivity.

Findings

Similar band structures in BLH and MLH.

Negligible $z$-direction dispersion in BLH.

Significant $z$-direction dispersion in MLH.

Abstract

To shed new light on the mechanism of superconductivity in sodium cobalt oxide bilayer-hydrate (BLH), we perform a density functional calculation with full structure optimization for BLH and its related nonsuperconducting phase, monolayer hydrate (MLH). We find that these hydrates have similar band structures, but a notable difference can be seen in the $a_{1g}$ band around the Fermi level. While its dispersion in the $z$ direction is negligibly small for BLH, it is of the order of 0.1 eV for MLH. This result implies that the three dimensional feature of the $a_{1g}$ band may be the origin for the absence of superconductivity in MLH.