Mass-enhanced Fermi-liquid ground state inNa1.5Co2O4

Magnetic, transport, and specific-heat measurements have been performed on layered metallic oxide ${\mathrm{Na}}_{1.5}{\mathrm{Co}}_2{\mathrm{O}}_4$ as a function of temperature T. Below a characteristic temperature $T^{*}=30\mathrm{}-40\mathrm{K},$ electrical resistivity shows a metallic conductivity with a $T^2$ behavior and magnetic susceptibility deviates from the Curie-Weiss behavior showing a broad peak at $\sim 14\mathrm{K}.$ The electronic specific-heat coefficient $\gamma$ is $\sim 60{\mathrm{m}\mathrm{J}/\mathrm{m}\mathrm{o}\mathrm{l}\mathrm{}\mathrm{K}}^2$ at 2 K. No evidence for magnetic ordering is found. These behaviors suggest the formation of mass-enhanced Fermi-liquid ground state analogous to that in d-electron heavy fermion compound ${\mathrm{LiV}}_2{\mathrm{O}}_4.$