20 research outputs found
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