Pseudogap Formation and Heavy-Carrier Dynamics in Intermediate-Valence YbAl₃

Abstract

Infrared optical conductivity [σ(ω)] of the intermediate valence compound YbAl3 has been measured at temperatures 8 K ≤ T ≤ 690 K to study its microscopic electronic structures. Despite the highly metallic characters of YbAl3, σ(ω) exhibits a clear pseudogap (strong depletion of spectral weight) of about 60 meV below 40 K. It also shows a strong mid-infrared peak centered at ∼ 0.25 eV. Energy-dependent effective mass and scattering rate of the carriers obtained from the data indicate the formation of a heavy-mass Fermi liquid state. These characteristic results are discussed in terms of the hybridization states between the Yb 4f and the conduction electrons. It is argued, in particular, that the pseudogap and the mid-infrared peak result from the indirect and the direct gaps, respectively, within the hybridization state.

Hot electron relaxation in the heavy-fermionYb1−xLuxAl3compound using femtosecond optical pump-probe spe

“…Furthermore, the relaxation dynamics bottleneck is expected to be governed by the gap minimum, therefore taking the uncertainties in the interpretation of both experimental results the agreement is reasonable. Given the fact, that the mid infrared peak at 0.25 eV, 18 which is in the intermediate-valence systems commonly interpreted as the direct optical transition across the hybridization gap, 2 is in YbAl 3 present way above room temperature, 18 it is expected that the same is true also for the indirect gap, as implied by the present study. Figure 3 presents the T dependence of , obtained by the single exponential fit, on a series of Yb 1−x Lu x Al 3 samples.…”

“…This value is lower than the values of the pseudogap obtained from the inelastic neutron-scattering data ͑30 meV͒, 17 as well as the value inferred from the optical conductivity data on YbAl 3 ͑60 meV͒. 18 The relationship between the observed pseudogaps in the spin ͑neutrons͒ and charge ͑optical͒ excitation spectra is unclear. On the other hand, the interpretation of the optical conductivity data is also not straightforward 18 since the indirect transitions are forbidden by the momentum conservation law.…”

Far-infrared optical conductivity of CeCu2Si2

“…The properties of the peak structure at around 13 meV are similar to those observed in other 4f -based correlated electron systems, notably in the Kondo-semiconductors YbB 12 [16] [18], and in the heavy-fermion systems YbRh 2 Si 2 and YbIr 2 Si 2 [2]. For the skutterudite heavyfermion system CeRu 4 Sb 12 a peak of similar type is not reported with comparable clarity [19] whereas in certain Ce-based Kondo semiconductors comparable structures where discussed in terms of a pseudogap opening in the heavy quasiparticle band [20].…”

Optical observation of non-Fermi-liquid behavior in the heavy fermion state ofYbRh2Si2

“…Moreover, a peak at around 0.2 eV, visible already at T = 300 K and gradually developing with decreasing temperature, appears beyond a pseudogap-like structure similar to that reported for several other Kondo-lattice systems. [8,12,15,17] Here we report the extension of our optical investigations down to energies of 2 meV and temperatures down to 0.4 K. This allowed us to obtain yet inaccessible information on the low-energy HF optical response of YbRh 2 Si 2 and provides a detailed characterization of the electrodynamic NFL properties. In particular the lowenergy heavy quasiparticle excitations could be analyzed within the extended Drude model which yields m * (ω, T ) and 1/τ (ω, T ).…”

“…The ( ω) 2 behavior is indicated in 1/τ (ω) of many renormalized LFL metals, e.g. YbAl 3 [15], CePd 3 [12], and CeAl 3 [13]. At the same time, m * (ω) increases with decreasing T and ω indicating the formation of heavy quasiparticles at low temperatures.…”