Elliptical hole pockets in the Fermi surfaces of unhydrated and hydrated sodium cobalt oxides

TL;DR

This paper provides experimental evidence for the existence of elliptical hole pockets in the Fermi surfaces of sodium cobalt oxides, which are believed to be crucial for understanding their superconductivity, using x-ray Compton scattering.

Contribution

It presents the first direct bulk measurement evidence confirming the elliptical Fermi surface pockets in sodium cobalt oxides.

Findings

Elliptical hole pockets exist in the Fermi surfaces.

Hydrated and unhydrated samples show similar Fermi surface features.

Supports theories linking these pockets to superconductivity.

Abstract

The surprise discovery of superconductivity below 5K in sodium cobalt oxides when hydrated with water has caught the attention of experimentalists and theorists alike. Most explanations for its occurence have focused heavily on the properties of some small elliptically shaped pockets predicted to be the electronically dominant Fermi surface sheet, but direct attempts to look for them have instead cast serious doubts over their existence. Here we present evidence that these pockets do indeed exist, based on bulk measurements of the electron momentum distribution in unhydrated and hydrated sodium cobalt oxides using the technique of x-ray Compton scattering.