Kondo effect in Ce(x)La(1-x)Cu(2.05)Si(2) intermetallics

The magnetic susceptibility and susceptibility anisotropy of the quasi-binary alloy system Ce(x)La(1-x)Cu(2.05)Si(2) have been studied for low concentration of Ce ions. The single-ion desc ription is found to be valid for x < 0.1. The experimental results are discussed in terms of t he degenerate Coqblin-Schrieffer model with a crystalline electric field splitting Delta = 330 K. The properties of the model, obtained by combining the lowest-order scaling and the pertur bation theory, provide a satisfactory description of the experimental data down to 30 K. The e xperimental results between 20 K and 2 K are explained by the exact solution of the Kondo mode l for an effective doublet.Comment: 11 pages, 13 Postscript figures, 1 tabl

Thermopower of CexR1-xB6 (R=La, Pr and Nd)

The thermopower, S, of CexR1-xB6 (R=La, Pr, Nd) was investigated. S with a positive sign shows a typical behavior observed in the Ce Kondo system, an increase with decreasing temperature at high temperatures and a maximum at low temperatures. The S values of all the systems at high temperatures are roughly linearly dependent on the Ce concentration, indicating the conservation of the single-impurity character of the Kondo effect in a wide x range. However, the maximum value of S, S_max, and the temperature, T_max, at which S_max is observed exhibit different x dependences between CexLa1-xB6 and CexR1-xB6 (R=Pr, Nd). In CexLa1-xB6, T_max, which is ~8 K in CeB6, decreases with decreasing x and converges to ~1 K in a very dilute alloy and S_max shows an increase below x ~ 0.1 after decreasing with decreasing x. In CexR1-xB6 (R=Pr, Nd), T_max shows a weak x dependence but S_max shows a roughly linear decrease in x. These results are discussed from the standpoint of the chemical pressure effect and the Ce-Ce interaction. S in the long-range ordered phase shows very different behavior between CexPr1-xB6 and CexNd1-xB6.Comment: PDF file, 7 pages with 9 figures, accepted for publicatio

Exact solution of the Falicov-Kimball model with dynamical mean-field theory

The Falicov-Kimball model was introduced in 1969 as a statistical model for metal-insulator transitions; it includes itinerant and localized electrons that mutually interact with a local Coulomb interaction and is the simplest model of electron correlations. It can be solved exactly with dynamical mean-field theory in the limit of large spatial dimensions which provides an interesting benchmark for the physics of locally correlated systems. In this review, we develop the formalism for solving the Falicov-Kimball model from a path-integral perspective, and provide a number of expressions for single and two-particle properties. We examine many important theoretical results that show the absence of fermi-liquid features and provide a detailed description of the static and dynamic correlation functions and of transport properties. The parameter space is rich and one finds a variety of many-body features like metal-insulator transitions, classical valence fluctuating transitions, metamagnetic transitions, charge density wave order-disorder transitions, and phase separation. At the same time, a number of experimental systems have been discovered that show anomalies related to Falicov-Kimball physics [including YbInCu4, EuNi2(Si[1-x]Gex)2, NiI2 and TaxN].Comment: 51 pages, 40 figures, submitted to Reviews of Modern Physic

Transport properties of Ni81.5B18.5 - YP y amorphous alloys

The thermoelectric power of the amorphous nonmagnetic alloy system Ni 81.5B18.5-yPy (y = 0, 1.8, 3.7, 7.4, 13, 16.8 and 18.5 at % P) has been investigated in the temperature range between 77 and 350 K. The resistivity and temperature coefficient of resistivity have also been measured. The high temperature slope of the thermopower, the resistivity and the room temperature coefficient of resistivity are simultaneously explained within the framework of the extended Ziman model. In performing the corresponding calculations we have chosen the phase shifts in a such a way that they reflect the d-band filling on alloying (deduced from the specific heat measurements). An unexpectedly large negative thermopower is obtained for the boron rich alloys. A possible origin of a « giant » contribution to the thermopower of these alloys is discussed.Nous avons étudié le pouvoir thermoélectrique (PTE) d'alliages amorphes non magnétiques Ni81,5B18,5-yPy (y = 0, 1,8, 3,7, 7,4,13,16,8 et 18,5 at % P) entre 77 K et 350 K ainsi que la résistivité et son coefficient de température. Nous interprétons simultanément ces propriétés dans le cadre d'un modèle de Ziman généralisé. Nous choisissons, pour ces calculs, des déphasages qui reflètent le remplissage de la bande d des alliages tel qu'on le déduit des mesures de chaleur spécifique. On obtient une surprenante contribution négative importante dans les alliages riches en bore. On discute l'origine possible d'une contribution géante au PTE de ces alliages