CoO2-Layer-Thickness Dependence of Magnetic Properties and Possible Two Different Superconducting States in NaxCoO2.yH2O

TL;DR

This study theoretically explores how CoO2-layer thickness influences magnetic and superconducting behaviors in NaxCoO2.yH2O, revealing layer-dependent magnetic fluctuations and two distinct superconducting states, aligning with experimental observations.

Contribution

It provides a theoretical analysis of layer-thickness effects on magnetic and superconducting phases, identifying two different SC states and explaining experimental phase diagrams.

Findings

Magnetic fluctuations depend strongly on layer thickness.

Two superconducting phases with different pairing symmetries are identified.

A triplet p-wave SC phase with dome-shaped Tc is predicted for s=+3.5.

Abstract

In order to understand the experimentally proposed phase diagrams of NaxCoO2.yH2O, we theoretically study the CoO2-layer-thickness dependence of magnetic and superconducting (SC) properties by analyzing a multiorbital Hubbard model using the random phase approximation. When the Co valence (s) is +3.4, we show that the magnetic fluctuation exhibits strong layer-thickness dependence where it is enhanced at finite (zero) momentum in the thicker (thinner) layer system. A magnetic order phase appears sandwiched by two SC phases, consistent with the experiments. These two SC phases have different pairing states where one is the singlet extended s-wave state and the other is the triplet p-wave state. On the other hand, only a triplet p-wave SC phase with dome-shaped behavior of Tc is predicted when s=+3.5, which is also consistent with the experiments. Controversial experimental results on the magnetic properties are also discussed.