Temperature dependence of low-energy optical conductivity of Yb ₄(As _1-xP _x) ₃ (x = 0, 0.05, 0.15)

To investigate the anomalous transport property and the electronic structure near the Fermi level of Yb ₄As ₃, we measured the temperature dependence of the reflectivity spectra of Yb ₄(As _1-xP _x) ₃ (x = 0, 0.05, 0.15) in the photon energy range of 2 meV 1.5 eV. The optical conductivity spectrum due to carrier absorption (Drude curve) significantly changes with temperature. Above 200 K, the Drude curve with a high effective carrier density (N _eff) and a short, relaxation time (τ) is commonly observed in all Yb ₄(As _1-xP _x) ₃. On the other hand, below 70 K, the Drude curve changes to one with a low N _eff and a long τ below 10 meV. At the same temperature, a new peak appears at 15 meV in Yb ₄As ₃. The Drude curve and the new peak are considered to originate from the bare As 4p hole band and the hybridization state between the 4f and 5d bands on the Yb ³⁺ chain, respectively.