Angle-resolved photoemission study of cobalt oxide superconductor NaxCoO2.yH2O : Observation of the Fermi surface

TL;DR

This study uses ARPES to analyze the electronic structure and Fermi surface of the cobalt oxide superconductor NaxCoO2.yH2O, revealing key features near the Fermi level relevant to its superconductivity.

Contribution

It provides the first detailed ARPES mapping of the Fermi surface and electronic structure of NaxCoO2.yH2O, highlighting differences from band calculations and previous studies.

Findings

Hexagonal Fermi surface centered at G point

Absence of small pocket Fermi surfaces along G-K

eg' band top close to Fermi level, within 20-50 meV

Abstract

Cobalt oxide superconductor NaxCoO2.yH2O is studied by angle-resolved photoemission spectroscopy (ARPES). We report the Fermi surface (FS) topology and electronic structure near the Fermi level (EF) of NaxCoO2.yH2O. Our result indicates the presence of the hexagonal FS centered at G point, while the small pocket FSs along G-K direction are absent similar to NaxCoO2. The top of the eg' band, which is expected in band calculations to form the small pocket FSs, extends to within 20 - 50 meV below EF, more closer to EF than in NaxCoO2. We discuss its possible role in superconductivity, comparing with other experimental and theoretical results.