Kondo-like behavior in a mixed valent oxypnictide La3Cu4P4O2

We have synthesized and characterized the physical properties of a layered, mixed valent oxypnictide La₃Cu₄P₄O₂ via magnetization, electrical resistivity, and specific heat measurements. Although La₃Cu₄P₄O₂ does not exhibit superconductivity down to T = 0.5 K, it demonstrates an intriguing resistivity minimum observed at Tₘᵢₙ = 13.7 K. Disappearance of the resistivity minimum under an applied magnetic field of μ ₀ H = 9 T together with the negative magnetoresistance at low and positive at high temperatures are observed, which are typical for both Kondo-like spin-dependent scattering and 3D weak localization. We argue that the Kondo scattering is a more plausible explanation due to the low-temperature deviation from the Curie-Weiss law observed in the magnetic susceptibility, consistent with the presence of magnetic interactions between paramagnetic Cu²⁺ ions and Kondo screening of these Cu²⁺ moments. We supplemented the experimental characterization with a detailed description of chemical bonding, employing density functional theory (DFT) calculations and crystal orbital Hamilton population (COHP) analysis for La₃Cu₄P₄O₂ and isostructural La₃Ni₄P₄O₂ , which is a superconductor with Tc = 2.2 K. Based on the calculations performed, we present the difference between La₃Cu₄P₄O₂ and La₃Ni₄P₄O₂ in the character of electronic states at the Fermi level. This discrepancy impacts structural stability and may cause a lack of superconductivity in La₃Cu₄P₄O₂ down to T = 0.5 K.