The heavy fermion compound YbAgCu4

Abstract

We re-examine the experimental data for the specific heat, the magnetic susceptibility, magnetization, and inelastic neutron scattering for the moderately heavy-electron compound YbAgCu4 within the framework of the single-ion Anderson model. Such an analysis has previously given excellent agreement between theory and experiment for numerous light heavy-fermion compounds. We extend here previous interpretations for the specific heat and magnetization within the Coqblin–Schrieffer model to a common set of model parameters by incorporating a weak valence admixture. The crystalline field splitting in this compound appears to be small compared to the Kondo temperature. Existing exact solutions of the Anderson model within the framework of Bethe’s ansatz are used for the thermodynamic properties. A simple resonant-level model is introduced to parametrize the Kondo resonance and to qualitatively interpret the inelastic neutron scattering cross section.

Physical properties ofYbXCu4(X=Ag,Au, Cd,

“…YbAgCu 4 is a prototypical heavy-Fermion compound that displays a linear specific heat coefficient ␥ above 200 mJ/mol K 2 with no magnetic order observed to the lowest temperatures measured. It has been claimed that the data for YbAgCu 4 can be fit quantitatively to the numerical predictions of the Jϭ7/2 Coqblin-Schrieffer model; [4][5][6][7][8] however, the characteristic temperatures that one extracts from fits to various physical properties of YbAgCu 4 display a large scatter. 9 In sharp contrast, YbAuCu 4 orders magnetically below 1 K, and its lowtemperature properties are dominated by long range Ruderman-Kittel-Kasuya-Yosida interactions and crystalelectric-field effects.…”

Evolution from first-order valence transition to heavy-fermion behavior inYbIn1−xSarrao1, Immer2, Benton3 et al. 1996Phys. Rev. B

“…4 and 5͒ is a moderately heavy ͑␥ ϭ250 mJ/mol K 2 ͒ mixed-valence compound whose susceptibility, field-dependent magnetization, and specific heat are consistent with a Jϭ7/2 Kondo impurity, as described by the Coqblin-Schrieffer model. 6,7 The prototypical example of the type of first-order isostructural valence transition observed in YbInCu 4 is the socalled ␥-␣ transition in elemental Ce ͑for a review, see, e.g., Refs. 8 and 9͒.…”

Pressure-Induced Superconductivity in Elemental Ytterbium Metal

“…these highly correlated electron phenomena. For example, an in-depth study of elemental Yb metal would directly aid our understanding of heavy fermion, quantum critical, non-Fermi liquid, magnetic ordering, and/or unconventional superconductivity in Yb-based compounds [9][10][11][12][13], and also enhance our understanding of these phenomena in general. Very recently β-YbAlB 4 [9] was reported to be the first superconducting Yb-based heavyfermion system, with T c = 80 mK.…”