Quantum critical behaviour in NaxCoO2

TL;DR

This paper presents evidence of a quantum phase transition in NaxCoO2 through divergence in susceptibility, suggesting magnetic fluctuations may influence superconductivity.

Contribution

It provides experimental evidence of a zero-temperature ferromagnetic phase transition and discusses the role of magnetic fluctuations in superconductivity.

Findings

Divergence of nonlinear susceptibility as T approaches 0 K.

Evidence for a quantum critical point at specific Na concentrations.

Scaling behavior of magnetization indicating local magnetic fluctuations.

Abstract

We report the divergence of the nonlinear component of the bulk susceptibility in NaxCoO2 (0.3<x<0.62) as T goes to 0 K. These experiments provide an striking evidence of the existence of a ferromagnetic phase transition at zero Kelvin (quantum phase transition). The possible role of magnetic fluctuations in the superconductivity is discussed to the light of the observed (H,T) scaling of the magnetization, which implies a local character of the fluctuations.