Possible quantum criticality inNaxCoO2

Abstract

A $(T,H)$ phase diagram of metallic ${\mathrm{Na}}_{x}\mathrm{Co}{\mathrm{O}}_{2}$ is proposed. At low Na content $(x\ensuremath{\approx}0.36)$, the magnetic susceptibility diverges with a power law ${T}^{\ensuremath{-}\ensuremath{\eta}}$ $(\ensuremath{\eta}<1)$ and shows $(T,H)$ scaling, indicating the proximity to a magnetic quantum phase transition. A magnetic field suppression of the low-temperature specific heat was observed for these compositions. At high Na content $(x\ensuremath{\approx}0.69)$ the susceptibility does not diverge, but renormalizes and becomes strongly field-dependent at low temperatures, forming a heavy Fermi liquid.