Bulk Electronic structure of Na$_{0.35}$CoO$_{2}$.1.3H$_{2}$O

TL;DR

This study uses high-energy synchrotron photoemission spectroscopy to analyze the bulk electronic structure of the layered superconductor Na$_{0.35}$CoO$_{2}$.1.3H$_{2}$O, revealing details about Co oxidation states and electronic correlations.

Contribution

It provides new insights into the electronic states and Coulomb interactions in Na$_{0.35}$CoO$_{2}$.1.3H$_{2}$O using advanced spectroscopic and theoretical methods.

Findings

Co 2p core levels show distinct Co$^{3+}$ and Co$^{4+}$ ions.

Cluster calculations indicate low spin states and moderate Coulomb energy U$_{dd}$.

Valence band PES aligns with band structure calculations.

Abstract

High-energy (h$\nu$ = 5.95 keV) synchrotron Photoemission spectroscopy (PES) is used to study bulk electronic structure of Na$_{0.35}$CoO$_{2}$.1.3H$_{2}$O, the layered superconductor. In contrast to 3-dimensional doped Co oxides, Co $\it{2p}$ core level spectra show well-separated Co$^{3+}$ and Co$^{4+}$ ions. Cluster calculations suggest low spin Co$^{3+}$ and Co$^{4+}$ character, and a moderate on-site Coulomb correlation energy U$_{dd}\sim$3-5.5 eV. Photon dependent valence band PES identifies Co $\it{3d}$ and O $\it{2p}$ derived states, in near agreement with band structure calculations.