Deformation of Electronic Structures Due to CoO6 Distortion and Phase Diagrams of NaxCoO2.yH2O

TL;DR

This study investigates how CoO6 distortion influences the electronic structure and phase behavior of NaxCoO2.yH2O, revealing deformation of bands and proposing phase diagrams with different superconducting and magnetic phases.

Contribution

It introduces a multiband tight-binding model based on LDA results to analyze CoO6 distortion effects and proposes schematic phase diagrams for different Co valence states.

Findings

Deformation of band dispersions with CoO6 distortion

Proposed phase diagram with three phases for s=+3.4

Alternative phase diagram with single phase for s=+3.5

Abstract

Motivated by recently reported experimental phase diagrams, we study the effects of CoO6 distortion on the electronic structure in NaxCoO2.yH2O. We construct the multiband tight-binding model by employing the LDA result. Analyzing this model, we show the deformation of band dispersions and Fermi-surface topology as functions of CoO2-layer thickness. Considering these results together with previous theoretical ones, we propose a possible schematic phase diagram with three successive phases: the extended s-wave superconductivity (SC), the magnetic order, and the spin-triplet SC phases when the Co valence number s is +3.4. A phase diagram with only one phase of spin-triplet SC is also proposed for the s=+3.5 case.