Fermi-liquid state and enhanced electron correlations in the iron pnictide CaFe₄ As₃

The recently discovered CaFe₄ As₃ system displays low-temperature Fermi-liquid behavior, with enhanced electron-electron correlations. At high temperatures, the magnetic susceptibility shows Curie-Weiss behavior, with a large temperature-independent contribution. Antiferromagnetic ordering is observed below TN = (88.0±1.0) K, possibly via a spin density wave transition. A remarkably sharp drop in resistivity occurs below T2 = (26.4±1.0) K, correlated with a similarly abrupt increase in the susceptibility but no visible feature in the specific heat. The electronic specific-heat coefficient γ at low temperatures is close to 0.02J mol Fe -1 K-2, but a higher value for γ∼0.08J mol Fe -1 K-2 can be inferred from a linear Cp/T vs T2 just above T2. The Kadowaki-Woods ratio A/ γ2 =55 10-5 μΩcm mol2 K2 mJ-2 is nearly two orders of magnitude larger than that of heavy fermions.