Ground state properties of the moderate heavy-fermion Kondo lattice Ce₂Rh₃Ga₉: Observation of a departure from Fermi-liquid type behavior

The ternary gallium-rich Y₂Co₃Ga₉-type compound, Ce₂Rh₃Ga₉ and its non-4 f-electron isostructural counterpart La₂Rh₃Ga₉ have been successfully synthesized using the conventional arc-melting method. The physical properties were determined by means of x-ray powder diffraction (XRD), magnetic susceptibility χ(T ), isothermal magnetization M(B), specific heat C_p(T ), electrical resistivity ρ(T ), and thermopower S(T) measurements. In addition, a first-principles density functional theory (DFT) investigations have been used to further explore the thermophysical and electron structure properties. The XRD crystal structure determination at room temperature has revealed that both compounds have the orthorhombic Y₂Co₃Ga₉-type crystal structure, with the space group Cmcm. χ(T ), C_p(T ), and ρ(T ) measurements performed in a wide temperature range reveal that La₂Rh₃Ga₉ is a weakly interacting, nonmagnetic metal with γ = 7.5 mJ/La-mol K². On the other hand, for Ce₂Rh₃Ga₉ the same measurements, plus S(T) uncover the features usually found in the heavy-fermion Kondo lattice class of materials with a strong impact of the crystal field effect (CEF). The characteristic parameters estimated for this material, such as Kondo temperature and the Sommerfeld coefficient, are respectively T_K = 14.7 K and γ = 100 mJ/Ce-mol K². Additionally, at low temperatures, the Ce-based compound is found to exhibit the −lnT behavior of the ratio C_p(T )/T, without exhibiting any phase transition down to 1.9 K. Also, the measurements of ρ(T ) performed down to 0.4 K showed no anomaly that might evidence the presence of a phase transition. Such a low-T logarithmic upturn in specific heat, together with the observed enhancement in the thermodynamic effective mass of the fermionic quasiparticles, as well as an anomalous power law temperature dependence of the ρ(T ) ∼ ρ_el-elT^1.5 signals Fermi liquid breakdown, likely connected to the presence of a quantum critical point at T → 0 K. The remarkably large values of the slope S(T )/T have also been noted for the low-T regime.