Far-infrared optical conductivity of CeCu₂Si₂

Abstract

Abstract.[Journal ref.: J. Phys.: Condens. Matter 25, 065602 (2013)] We investigated the optical reflectivity of the heavy-fermion metal CeCu 2 Si 2 in the energy range 3 meV -30 eV for temperatures between 4K -300K. The results for the charge dynamics indicate a behavior that is expected for the formation of a coherent heavy quasiparticle state: Upon cooling the spectra of the optical conductivity indicate a narrowing of the coherent response. Below temperatures of 30 K a considerable suppression of conductivity evolves below a peak structure at 13 meV. We assign this gap-like feature to strong electron correlations due to the 4f -conduction electron hybridization.

Optical Evidence of Itinerant-Localized Crossover of 4fElectrons in Cerium Compounds

“…To obtain σ(ω) via the KKA of R(ω), the spectra were extrapolated to below 2 meV with a Hagen-Rubens function and to above 30 eV with the free-electron approximation R(ω) ∝ ω −4 . 18 σ(ω) spectra of polycrystalline CeM 2 Ge 2 as well as single-crystalline CeCu 2 Si 2 19 and polycrystalline CeM Ge 2 s (M = Co, Ni) 20 were compared with the unoccupied density of states (DOS) obtained from the LDA band structure calculation including spin-orbit coupling using the Wien2k code. 21 All experimental spectra were taken at a temperature of 8-10 K. Figure 2a shows the σ(ω) spectra derived from the KKA of R(ω) spectra and the unoccupied DOS.…”

Optical evidence of local and itinerant states in Ce- and Yb-heavy-fermion compounds

“…σ(ω) spectra of CeM 2 Ge 2 at 8-10 K have already been reported [23]. In this paper, we will report the temperature-dependent σ(ω) spectra of CeM 2 Ge 2 and Yb(Co x Rh 1−x ) 2 Si 2 (x = 0, 0.27) compared with those of CeCu 2 Si 2 [38], YbRh 2 Si 2 [39], and YbIr 2 Si 2 [40] to check the relation of the Kondo temperature to the temperature-dependent spectral change. The spectrum of CeCu 2 Si 2 was taken from Ref.…”

“…The spectrum of CeCu 2 Si 2 was taken from Ref. [38]. The baselines of each R(ω) and σ(ω) spectra are shifted by 0.15 and 4.5 × 10 3 Ω −1 cm −1 , respectively.…”

“…Figure 2. Temperature-dependent optical reflectivity (R(ω) ) spectra (a) and optical conductivity (σ(ω)) spectra (b) of CeM 2 Ge 2 (M =Ag, Rh, Ru, Cu, Ni) and CeCu 2 Si 2 .The spectrum of CeCu 2 Si 2 was taken from Ref [38]…”

Optical study on electronic structure of the locally non-centrosymmetric CeRh$_2$As$_2$

“…Figure 8 shows the temperature dependencies of the center of gravity [∆ ω = [ ω(T ) − ω(300 K) ] / ω(300 K) ], where ω(T ) = ω2 ω1 ωσ 1 (ω)dω/ ω2 ω1 σ 1 (ω)dω, and the spectral weight transfer [∆SW = ω2 ω1 [|σ 1 (ω, T ) − σ 1 (ω, 300 K)|/σ 1 (ω, 300 K)]dω] of the mid-IR peak of CeRh 2 As 2 relative to those at T = 300 K. The integration range was set as ω 1 = 0 eV ≤ ω ≤ ω 2 = 0.8 eV, where the spectral change in the lower energy region is almost recovered. In the figure, the evaluated ∆ ω and ∆SW of two heavy-fermion compounds CeCu 2 Si 2 (T K ∼ 10 K) [36] and CeNi 2 Ge 2 (T K ∼ several K) [33] are also plotted for comparison. The temperature dependencies of ∆ ω and ∆SW correspond to the evolution of the c-f hybridization with temperature [31], i.e., an increasing itinerancy corresponds to increasing values of ∆ ω and ∆SW whereas constant values suggest a localization of the 4f state.…”