Terahertz Electrodynamics of Mixed-Valent YbAl3 and LuAl3 Thin Films
Abstract
We present THz measurements of thin films of mixed-valent YbAl3 and its structural analogue LuAl3. Combined with traditional Fourier transform infrared (FTIR) spectroscopy, the extended Drude formalism is utilized to study the low-frequency transport of these materials. We find that LuAl3 demonstrates conventional Drude transport whereas at low temperatures YbAl3 demonstrates a sharply renormalized Drude peak and a mid-infrared (MIR) peak in the conductivity, indicative of the formation of a heavy Fermi liquid. In YbAl3 the extended Drude framework shows a consistency of the scattering rate with Fermi-liquid behavior below T < 40 K and a moderate mass enhancement. While a ω2 Fermi liquid-like frequency dependence is not clearly exhibited, the temperature dependence of the Drude scattering rate and effective mass is consistent with the formation of a low-temperature moderately heavy Fermi liquid, albeit one with a smaller mass than observed in single crystals. The extended Drude analysis also supports a slow crossover between the Fermi liquid state and the normal state in YbAl3.