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

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

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

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

Diffusion Thermopower at Even Denominator Fractions

We compute the electron diffusion thermopower at compressible Quantum Hall states corresponding to even denominator fractions in the framework of the composite fermion approach. It is shown that the deviation from the linear low temperature behavior of the termopower is dominated by the logarithmic temperature corrections to the conductivity and not to the thermoelectric coefficient, although such terms are present in both quantities. The enhanced magnitude of this effect compared to the zero field case may allow its observation with the existing experimental techniques.Comment: Latex, 12 pages, Nordita repor

On the low energy properies of fermions with singular interactions

We calculate the fermion Green function and particle-hole susceptibilities for a degenerate two-dimensional fermion system with a singular gauge interaction. We show that this is a strong coupling problem, with no small parameter other than the fermion spin degeneracy, N. We consider two interactions, one arising in the context of the $t-J$ model and the other in the theory of half-filled Landau level. For the fermion self energy we show in contrast to previous claims that the qualitative behavior found in the leading order of perturbation theory is preserved to all orders in the interaction. The susceptibility $\chi_Q$ at a general wavevector $\bf{Q} \neq 2\bf{p_F}$ retains the fermi-liquid form. However the $2p_F$ susceptibility $\chi_{2p_F}$ either diverges as $T -> 0$ or remains finite but with nonanalytic wavevector, frequency and temperature dependence. We express our results in the language of recently discussed scaling theories, give the fixed-point action, and show that at this fixed point the fermion-gauge-field interaction is marginal in $d=2$, but irrelevant at low energies in $d \ge 2$.Comment: 21 pages, uuencoded LATEX file with included Postscript figures, R

Non-Fermi Liquid Behavior In Quantum Critical Systems

The problem of an electron gas interacting via exchanging transverse gauge bosons is studied using the renormalization group method. The long wavelength behavior of the gauge field is shown to be in the Gaussian universality class with a dynamical exponent $z=3$ in dimensions $D \geq 2$. This implies that the gauge coupling constant is exactly marginal. Scattering of the electrons by the gauge mode leads to non-Fermi liquid behavior in $D \leq 3$. The asymptotic electron and gauge Green's functions, interaction vertex, specific heat and resistivity are presented.Comment: 9 pages in REVTEX 2.0. Submitted to Phys. Rev. Lett. 3 figures in postscript files can be obtained at [email protected]. The filename is gan.figures.tar.z and it's compressed. You can uncompress it by using commands: "uncompress gan.figures.tar.z" and "tar xvf gan.figures.tar

Magnetic-field-induced Luttinger liquid

It is shown that a strong magnetic field applied to a bulk metal induces a Luttinger-liquid phase. This phase is characterized by the zero-bias anomaly in tunneling: the tunneling conductance scales as a power-law of voltage or temperature. The tunneling exponent increases with the magnetic field as BlnB. The zero-bias anomaly is most pronounced for tunneling with the field applied perpendicular to the plane of the tunneling junction.Comment: a reference added, minor typos correcte