Heavy quasiparticles and pseudogap formation in YbAl3:: Optical conductivity study

We have measured the optical conductivity sigma(omega) of the mixed-valent compound YbAl3. sigma(omega) exhibits a mid-infrared peak centered at 0.15-0.2 eV, which becomes more pronounced with decreasing temperature (T). In addition, a strong depletion of the spectral weight, i.e., a pseudogap formation, is observed in sigma(omega) below similar to0.1 eV. A comparison of sigma(omega) with the dc conductivity indicates the existence of an extremely narrow Drude peak at very low energy. Energy-dependent effective mass and scattering rate of the carriers are evaluated from the optical data, which indicates the formation of a heavy-mass Fermi liquid state within similar to40 meV from the Fermi level. These observations are discussed in terms of the hybridization of a conduction band and a narrow 4f band.