Electron energy relaxation by phonons in the Kondo condensate

We have used normal metal-insulator-superconductor tunnel junctions as thermometers at sub-Kelvin temperatures to study the electron-phonon (e-p) interaction in thin Aluminum films doped with Manganese, as a function of Manganese concentration. Mn in Al is known to be a Kondo impurity with extremely high Kondo temperature $T_K \sim$ 500 K, thus our results probe the e-p coupling in the fully spin compensated, unitary limit. The temperature dependence of the e-p interaction is consistent with the existing theory for disordered metals, however full theory including the Kondo effect has not been worked out yet. The strength of the interaction decreases with increasing Manganese concentration, providing a means to improve sensitivity of detectors and efficiency of solid state coolers

Screening effects in the electron-optical phonon interaction

We show that recently reported unusual hardening of optical phonons renormalized by the electron-phonon interaction is due to the neglect of screening effects. When the electron-ion interaction is properly screened optical phonons soften in three dimension. It is important that for short-wavelength optical phonons screening is static while for long-wavelength optical phonons screening is dynamic. In two-dimensional and one-dimensional cases due to crossing of the nonperturbed optical mode with gapless plasmons the spectrum of renormalized optical phonon-plasmon mode shows split momentum dependence.Comment: 7 page

Weak localization effect on thermomagnetic phenomena

The quantum transport equation (QTE) is extended to study weak localization (WL) effects on galvanomagnetic and thermomagnetic phenomena. QTE has many advantages over the linear response method (LRM): (i) particle-hole asymmetry which is necessary for the Hall effect is taken into account by the nonequilibrium distribution function, while LRM requires expansion near the Fermi surface, (ii) when calculating response to the temperature gradient, the problem of WL correction to the heat current operator is avoided, (iii) magnetic field is directly introduced to QTE, while the LRM deals with the vector potential and and special attention should be paid to maintain gauge invariance, e.g. when calculating the Nernst effect the heat current operator should be modified to include the external magnetic field. We reproduce in a very compact form known results for the conductivity, the Hall and the thermoelectric effects and then we study our main problem, WL correction to the Nernst coefficient (transverse thermopower).Comment: 20 pages 2 figure

Coherent description of electrical and thermal impurity-and-phonon limited transport in simple metals

The electrical resistivity, thermoelectric power and electronic thermal conductivity of simple (isotropic) metals are studied in a uniform way. Starting from results of a variational solution of the Boltzmann equation, a generalized Matthiessen rule is used in order to superpose the inelastic (or not) electron-phonon and elastic electron-impurity scattering cross sections ("matrix elements"). The temperature dependence relative to these processes is given through simple functions and physical parameters over the usually investigated range of temperature for each transport coefficient. The coherence of such results is emphasized.Comment: 22 pages, 5 figures; to appear in International Journal of Modern Physics

Contribution à la connaissance de la typologie ichthyenne des rivières ardennaises

Les auteurs, disposant d'un ensemble de données quantitatives concernant des populations de poissons issus d'un même contexte biogéographique, l'Ardenne belge, leur appliquent divers traitements mathématiques dans le but de connaître celui(ceux) qui perme(tten)t de préciser l'existence de groupements Ichthyens (hiérarchisation de 2° ordre).Il en ressort que l'analyse des fréquences relatives des espèces en chaque station par la méthode des composantes principales, met en évidence les structures biotypologiques et leurs relations :- le classement structurel des eaux torrentielles ne dépend que d'un paramètre lié fortement à la vitesse du courant (en relation avec la pente). - le classement structurel des eaux modérées à lentes est étroitement lié à un paramètre de limnophilie, complété de 2 paramètres probables demeurant à déterminer.Les auteurs proposent, pour le rhitron et le potamon supérieur des affluents ardennais de la Meuse et du Rhin belges :• un essai de typologie basé sur l'existence de groupes socio-écologiques de poissons téléostéens, définis au mieux comme suit :- Rhéophile           supra             truite, chabot                             médio            vairon, loche franche                             infra              ombre, goujon, chevesne- Limnophile          supra             hotu, vandoise, barbeau, gardon                             médio            tanche (réserves pour échantillonnage trop faible) ;• une méthodologie de détermination du niveau typologique pour le rhitron et l'épipotamon ;• les limites d'extension des zones typologiques obtenues.Quantitative data about fish populations from a homogeneous biogeographical environment, the Belgian Ardenne rivera, have been subjected to statistical analysis. This analysis was designed to determine which statistical method(s) could be used to identify ichthyological groups (second-ordre hierarchy).Electro-fishing data were available for 140 sites ; elimination of polluted stations left 98 sites, and of these 84 were used for the statistical analysis. Four matrices were constructed frome the raw data : absolute and relative species frequencies ; absolute and relative species biomasses. Correlation coefficients were used together with a hierarchical ranking method, based on chaining and principal component analysis (PCA). Methodological variations involved the selected data basic, selection of distance, species position criteria and chaining method.Application of PCA to the species frequency data yielded a primary axis (33 % explained variance) which separated suprarheophilic and limnophilic species. The second, third and fourth axes explained 14, 10 and 8 % of the variance, respectively. Similarly, PCA analysis of the biomass data yielded a primary axis (25 % explained variance) separating suprarheophilic and moderate-water species. The second, third and fourth axes explained 13, 10 and 8 % al the variance. Projection of the structure in the 1-2-3 numerical sub-space (57 % of the information) is very expressive.Hierarchical analysis of the proximity of different species led to the définition of the following socio-ecological groups :- Rheophilic    supra    brown trout, bullhead    medio    minnow, stone-loach    infra    grayling, gudgeon, chub- Limnophilic    supra    common nose, dace, barbet, roach    medio    tench (with reserves)Hierarchical analysis of the proximity between stations confirms, in the 2-4 space of the first PC analysis, these same divisions.In conclusion, the PC analysis of the relative occurrence of the various species at each station reveals the biogeographical structures and their relations. The structural ranking of the torrential waters depends on a single parameter, strongly related to the flow velocity (in relation to the bed slope). The structural ranking of the moderate to slow-moving waters is strongly related to a limnophilic parameter, likely associated with two other unknown parameters (to be determined). A typological level determination is proposed for the rhitron and epipotamon, as are the extension limits for the defined typological zones

Coulomb blockade in quantum dots under AC pumping

We study conductance through a quantum dot under Coulomb blockade conditions in the presence of an external periodic perturbation. The stationary state is determined by the balance between the heating of the dot electrons by the perturbation and cooling. We analyze two cooling mechanisms: electron exchange with the cold contacts and emission of phonons. Together with the usual linear Ohmic heating of the dot electrons we consider possible effects of dynamic localization. The combination of the abovementioned factors may result in a drastic change of the shape of the Coulomb blockade peak with respect to the usual equilibrium one.Comment: 12 pages, 8 figure

Disorder-Assisted Electron-Phonon Scattering and Cooling Pathways in Graphene

We predict that graphene is a unique system where disorder-assisted scattering (supercollisions) dominates electron-lattice cooling over a wide range of temperatures, up to room temperature. This is so because for momentum-conserving electron-phonon scattering the energy transfer per collision is severely constrained due to a small Fermi surface size. The characteristic $T^3$ temperature dependence and power-law cooling dynamics provide clear experimental signatures of this new cooling mechanism. The cooling rate can be changed by orders of magnitude by varying the amount of disorder which offers means for a variety of new applications that rely on hot-carrier transport.Comment: 4 pgs, 2 fg

Magnetoresistance, noise properties and the Koshino-Taylor effect in the quasi-1D oxide KRu_4O_8

The low temperature electronic and galvanomagnetic transport properties of the low dimensional oxide KRu_4O_8 are experimentally considered. A quadratic temperature variation of the resistivity is observed to be proportional to the residual resistivity. It shows the role of inelastic electron scattering against impurities, i.e. a large Koshino-Taylor effect, rather than a consequence of strong electronic correlations. In the same temperature range, the Kohler rule is not fulfilled. The resistance noise increases also sharply, possibly due to a strong coupling of carriers with lattice fluctuations in this low dimensional compound.Comment: accepted for publication in Europhysics Lette

Recombination limited energy relaxation in a BCS superconductor

We study quasiparticle energy relaxation at sub-kelvin temperatures by injecting hot electrons into an aluminium island and measuring the energy flux from electrons into phonons both in the superconducting and in the normal state. The data show strong reduction of the flux at low temperatures in the superconducting state, in qualitative agreement with the presented quasiclassical theory for clean superconductors. Quantitatively, the energy flux exceeds that from the theory both in the superconducting and in the normal state, possibly suggesting an enhanced or additional relaxation process

Superconductivity by long-range color magnetic interaction in high-density quark matter

We argue that in quark matter at high densities, the color magnetic field remains unscreened and leads to the phenomenon of color superconductivity. Using the renormalization group near the Fermi surface, we find that the long-range nature of the magnetic interaction changes the asymptotic behavior of the gap $\Delta$ at large chemical potential $\mu$ qualitatively. We find $\Delta\sim\mu g^{-5}\exp(-{3\pi^2\over\sqrt{2}}{1\over g})$, where $g$ is the small gauge coupling. We discuss the possibility of breaking rotational symmetry by the formation of a condensate with nonzero angular momentum, as well as interesting parallels to some condensed matter systems with long-range forces.Comment: 14 pages, REVTEX, uses eps