New low-temperature phases in NaxCoO2 linked to quantum criticality

TL;DR

This study uncovers new electronic phases in NaxCoO2, revealing quantum criticality at low Na-content and heavy Fermi-liquid behavior at higher Na-content, suggesting potential for magnetically mediated superconductivity.

Contribution

It identifies and characterizes low-temperature phases in NaxCoO2 linked to quantum criticality and heavy Fermi-liquid formation, providing insights into its phase diagram.

Findings

Magnetic susceptibility diverges at x=0.36, indicating quantum criticality.

Heavy Fermi-liquid behavior observed at x=0.6 with field-dependent quasiparticle mass.

NaxCoO2 is a candidate for magnetically mediated superconductivity.

Abstract

New electronic phases have been identified and placed in the (T,H) phase diagram of metallic NaxCoO2. At low Na-content (x = 0.36), the magnetic susceptibility diverges with a power law T^(-n), n<1, and shows (T,H) scaling, indicating the proximity to a magnetic quantum phase transition. At high Na contents (x = 0.6) the mass of the quasiparticles does never diverge, but renormalizes and becomes strongly field dependent at low temperatures, forming a heavy Fermi-Liquid. Our results make superconducting NaxCoO2 a clear candidate for magnetically mediated pairing.