Selection Rules for Two Channel Kondo Models of U and Ce ions in Metals

Symmetry based selection rules are developed providing minimal criteria for the existence of two-channel Kondo interactions between conduction electrons and the low energy degrees of freedom on U$^{4+}$ and Ce$^{3+}$ in a metal host, assuming that the underlying microscopics are regulated by the Anderson Hamiltonian. An additional dynamic selection rule is imposed on Ce$^{3+}$ ions. The selection rules restrict the two-channel quadrupolar Kondo effect to U$^{4+}$ ions in cubic, tetragonal, and hexagonal symmetry. For hexagonal and tetragonal symmetry, the Kondo effect for a U$^{4+}$ ion will always be quadrupolar. The selection rules for Ce$^{3+}$ ions restrict the two-channel magnetic Kondo effect to one of three possible doublet ionic ground states in hexagonal symmetry and the lone doublet ionic ground state in cubic symmetry. The dynamical selection rule apparently excludes two-channel Kondo behavior for Yb$^{3+}$ ions.Comment: (16 pages, 2 figures) [Figures in usable postscript shell now

Landau and dynamical instabilities of Bose-Einstein condensates with superfluid flow in a Kronig-Penney potential

We study the elementary excitations of Bose-Einstein condensates in a one-dimensional periodic potential and discuss the stability of superfluid flow based on the Kronig-Penney model. We analytically solve the Bogoliubov equations and calculate the excitation spectrum. The Landau and dynamical instabilities occur in the first condensate band when the superfluid velocity exceeds certain critical values, which agrees with the result of condensates in a sinusoidal potential. It is found that the onset of the Landau instability coincides with the point where the perfect transmission of low-energy excitations is forbidden, while the dynamical instability occurs when the effective mass is negative. It is well known that the condensate band has a peculiar structure called swallowtail when the periodic potential is shallow compared to the mean field energy. We find that the upper side of the swallowtail is dynamically unstable although the excitations have the linear dispersion reflecting the positive effective mass.Comment: 6 pages, 2 figures, Proceedings of the International Symposium on Quantum Fluids and Solids (QFS2006

Anderson-Yuval approach to the multichannel Kondo problem

We analyze the structure of the perturbation expansion of the general multichannel Kondo model with channel anisotropic exchange couplings and in the presence of an external magnetic field, generalizing to this case the Anderson-Yuval technique. For two channels, we are able to map the Kondo model onto a generalized resonant level model. Limiting cases in which the equivalent resonant level model is solvable are identified. The solution correctly captures the properties of the two channel Kondo model, and also allows an analytic description of the cross-over from the non Fermi liquid to the Fermi liquid behavior caused by the channel anisotropy.Comment: 23 pages, ReVTeX, 4 figures av. on reques

Multi-Channel Kondo Necklace

A multi--channel generalization of Doniach's Kondo necklace model is formulated, and its phase diagram studied in the mean--field approximation. Our intention is to introduce the possible simplest model which displays some of the features expected from the overscreened Kondo lattice. The $N$ conduction electron channels are represented by $N$ sets of pseudospins \vt_{j}, $j=1, ... , N$, which are all antiferromagnetically coupled to a periodic array of |\vs|=1/2 spins. Exploiting permutation symmetry in the channel index $j$ allows us to write down the self--consistency equation for general $N$. For $N>2$, we find that the critical temperature is rising with increasing Kondo interaction; we interpret this effect by pointing out that the Kondo coupling creates the composite pseudospin objects which undergo an ordering transition. The relevance of our findings to the underlying fermionic multi--channel problem is discussed.Comment: 29 pages (2 figures upon request from [email protected]), LATEX, submitted for publicatio

Anomalous heavy-fermion and ordered states in the filled skutterudite PrFe4P12

Specific heat and magnetization measurements have been performed on high-quality single crystals of filled-skutterudite PrFe_4P_{12} in order to study the high-field heavy-fermion state (HFS) and low-field ordered state (ODS). From a broad hump observed in C/T vs T in HFS for magnetic fields applied along the direction, the Kondo temperature of ~ 9 K and the existence of ferromagnetic Pr-Pr interactions are deduced. The {141}-Pr nuclear Schottky contribution, which works as a highly-sensitive on-site probe for the Pr magnetic moment, sets an upper bound for the ordered moment as ~ 0.03 \mu_B/Pr-ion. This fact strongly indicates that the primary order parameter in the ODS is nonmagnetic and most probably of quadrupolar origin, combined with other experimental facts. Significantly suppressed heavy-fermion behavior in the ODS suggests a possibility that the quadrupolar degrees of freedom is essential for the heavy quasiparticle band formation in the HFS. Possible crystalline-electric-field level schemes estimated from the anisotropy in the magnetization are consistent with this conjecture.Comment: 7 pages and 7 figures. Accepted for publication in Phys. Rev.

Transition from a strong-coupling fixed point to an intermediate-coupling fixed point in a single-channel SU(N) Kondo model: role of the filling and two-stage screening

We study an extended SU(N) single-impurity Kondo model in which the impurity spin is described by a combination of Abrikosov fermions and Schwinger bosons. Our aim is to describe both the quasiparticle-like excitations and the locally critical modes observed in various physical situations, including non-Fermi liquid behavior in heavy fermion systems in the vicinity of a quantum critical point. We identify the strong coupling fixed point of the model and study its stability within second order perturbation theory. Already in the single channel case and in contrast with either the pure bosonic or the pure fermionic case, the strong coupling fixed point is unstable against the conduction electron kinetic term as soon as the amount of Abrikosov fermions reaches a critical value. In the stability region, the partially screened, dressed impurity at site 0 repels the conduction electrons on adjacent sites. In the instability region, the impurity tends to attract $(N-1)$ conduction electrons to the neighboring sites, giving rise to a two-stage Kondo effect with additional screening.This result opens the route to the existence of an intermediate coupling fixed point, characterized by non-Fermi liquid behavior

Patogenicidade de Corynespora cassiicola em soja, limiares térmicos e temperatura ótima para a germinação de conídios em meio de cultura Pathogenicity, thermal thresholds and optimal temperature for Corynespora cassiicola conidium germination in culture medium

Ensaios em câmara climatizada e laboratório, foram conduzidos para demonstrar a patogenicidade de Corynespora cassiicola em soja. Para esse estudo, utilizou-se um isolado monosporico obtido de folhas de soja de Primavera do Leste, MT. Os conídios analisados ao mi croscópio ótico a presentaram morfologia semelhante a do gênero Corynespora. A mensuração de 200 conídios desenvolvidos em meio de cultura, obteve-se as seguintes medidas 8-12 x 20 - 280 µm, média de 10 x 150 µm. O isolado foi inoculado no cultivar CD 219 RR para comprovar a sua patogenicidade. Pela comparação dos sintomas com as descrições da literatura e pelo reisolamento do patógeno, seguido de sua caracterização morfológica, confirmou-se à patogenicidade do isolado de C. cassiicola. Para identificar os limiares térmicos inferior (Lti) e superior (Lts) e a temperatura ótima e o limiar térmico superior (Lt s) para a germinação de esporos de C. cassiicola, foi conduzido um ensaio em placas de Petri, com meio de cultur a Czapekága r. Foram testados: ( a ) tempo de exposiçã o de 6 , 1 2 e 24 hora s e (b) temperaturas mínimas de 5, 6, 7, 8, 9 e 10 ºC, intermediárias de 15, 20, 25, 30 e 35ºC e superiores de 36, 37, 38, 39, 40 e 41ºC. Os dados foram submetidos a análise de variância e regressão. Os conídios germinaram em uma ampla gama de tempera tura tendo como valores de Lti 7ºC, ótima de 23ºC e valores de Lts 39ºC.<br>In experiments conducted in a growth chamber, the pathogenicity of a monosporic isolate of Corynespora cassiicola was tested. The isolate was obtained from the leaves of soybean was performed. The isolate of C. cassiicola used was obtained from leaves of soybean from Primavera do Leste, Mato Grosso State, Brazil. The morphology of the conidia under the optical microscope was similar to that of the genus Corynespora. In the assessment of 200 conidia, the following measures were obtained: 8-12 x 20 -280 m, mean of 10 x 150 µm. T he cultivar CD 219 RR was inoculated to prove pathogenicity. Based on the comparison of the symptoms with the descriptions in literature and on the pathogen reisolations followed by its morphological characterization, the pathogenicity of the C. cassiicola isolate used in this work is confirmed. To identify the lower (Lti), and upper (Lts) thermal threshold, as well as the optimal temperature, for the germination of spores, an experiment was performed in Petri dishes containing Czapek agar medium. The tested variables were: (a) exposure times of 6, 12 and 24 hours and (b) low temperatures of 5, 6, 7, 8, 9 and 10ºC, intermediate temperatures of 10, 15, 20, 25, 30 and 35ºC, and high temperatures of 36, 37, 38, 39, 40 and 41ºC. Data were subjected to analysis of variance and regression. The conidia germinated within a wide temperature range presenting Lti of 7ºC, optimal temperature of 23ºC and Lts of 39ºC