Anisotropic Non-Fermi Liquid and Dynamical Planckian Scaling of Quasi-Kagome Kondo Lattice Systems

At the quantum critical point between a magnetically ordered state and a correlated Fermi liquid state, a non-Fermi liquid state appears where electron correlations continuously develop to very low temperatures. The interacted electrons, namely quasiparticles, can be regarded as quantum entanglement where the relaxation time is scaled with the Planckian time, ℏ/k_BT. However, there is a debate over whether heavy-fermion systems can obey the Planckian time. In the optical conductivity spectra, the Planckian scale appears the scaling of ℏω/k_BT as the dynamical Planckian scaling (DPS). Here, we investigate the non-Fermi liquid behavior in the Drude response of a candidate for such materials, the quasi-kagome Kondo lattice CeMSn (M = Rh, Ir), combining polarized optical conductivity measurements and first-principles band calculations. Even though the material shows a strong valence fluctuation, renormalized Drude responses observed at the photon energy below 100 meV are characterized by non-Fermi-liquid-like scattering rate 1/τ which is far from other Ce-based heavy fermions. Additionally, the heavy carriers’ Drude response only for the Ce quasi-kagome plane obeyed DPS, suggesting quantum criticality. These results suggest that the anisotropic quantum criticality with the strong c-f hybridization is realized in the Ce quasi-kagome lattice systems.