Mass-enhanced Fermi-liquid ground state in Na1.5Co2O4

Magnetic, transport, and specific-heat measurements have been performed on layered metallic oxide Na 1 . 5 Co 2 O 4 as a function of temperature T. Below a characteristic temperature T*=30-40 K, electrical resistivity showsa metallic conductivity with a T 2 behavior and magnetic susceptibility deviates from the Curie-Weiss behavior showing a broad peak at ∼14 K. The electronic specific-heat coefficient y is ∼60 mJ/mol 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 LiV 2 O 4 .

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