A Fermi Sea of Heavy Electrons (a Kondo Lattice) is Never a Fermi Liquid

I demonstrate a contradiction which arises if we assume that the Fermi surface in a heavy electron metal represents a finite jump in occupancy

The Hubbard Model at Infinite Dimensions: Thermodynamic and Transport Properties

We present results on thermodynamic quantities, resistivity and optical conductivity for the Hubbard model on a simple hypercubic lattice in infinite dimensions. Our results for the paramagnetic phase display the features expected from an intuitive analysis of the one-particle spectra and substantiate the similarity of the physics of the Hubbard model to those of heavy fermion systems. The calculations were performed using an approximate solution to the single-impurity Anderson model, which is the key quantity entering the solution of the Hubbard model in this limit. To establish the quality of this approximation we compare its results, together with those obtained from two other widely used methods, to essentially exact quantum Monte Carlo results.Comment: 29 pages, 16 figure

Climatologies of streamer events derived from a transport model and a coupled chemistry-climate model

International audienceStreamers, i.e. finger-like structures, reach from lower into extra-tropical latitudes. They can be detected in N2O or O3 distributions on single lower stratospheric layers in mid-latitudes since they are characterised by high N2O or low O3 values compared to undisturbed mid-latitude values. If irreversible mixing occurs, streamer events significantly contribute to the transfer of tropical air masses to mid-latitudes which is also an exchange of upper tropospheric and stratospheric air. A climatology of streamer events has been established, employing the chemical-transport model KASIMA, which is driven by ECMWF re-analyses (ERA) and operational analyses. For the first time, the seasonal and the geographical distribution of streamer frequencies has been determined on the basis of 9 years of observations. For the current investigation, a meridional gradient criterion has been newly formulated and applied to the N2O distributions calculated with KASIMA. The climatology has been derived by counting all streamer events between 21 and 25 km for the years 1990 to 1998. It has been further used for the validation of a streamer climatology which has been established in the same way employing data of a multi-year simulation with the coupled chemistry-climate model ECHAM4.L39(DLR)/CHEM (E39/C). It turned out that both climatologies are qualitatively in fair agreement, in particular in the northern hemisphere, where much higher streamer frequencies are found in winter than in summer. In the southern hemisphere, KASIMA analyses indicate strongest streamer activity in September. E39/C streamer frequencies clearly offers an offset from June to October, pointing to model deficiencies with respect to tropospheric dynamics. KASIMA and E39/C results fairly agree from November to May. Some of the findings give strong indications that the streamer events found in the altitude region between 21 and 25 km are mainly forced from the troposphere and are not directly related to the dynamics of the stratosphere, in particular not to the dynamics of the polar vortex. Sensitivity simulations with E39/C, which represent recent and possible future atmospheric conditions, have been employed to answer the question how climate change would alter streamer frequencies. It is shown that the seasonal cycle does not change but that significant changes occur in months of minimum and maximum streamer frequencies. This could have an impact on mid-latitude distribution of chemical tracers and compounds. The influence of streamers on the mid-latitude ozone budget has been assessed by applying a special E39/C model configuration. The streamer transport of low ozone is simply inhibited by filling up its ozone content according to the surrounding air masses. It shows that the importance of streamers for the ozone budget strongly decreases with altitude. At 15 km streamers lead to a decrease of ozone by 80%, whereas around 25 km it is only 1 to 5% and at mid-latitude tropopause, ozone decreases by 30% (summer) to 50% (winter)

Zeros of the Partition Function and Pseudospinodals in Long-Range Ising Models

The relation between the zeros of the partition function and spinodal critical points in Ising models with long-range interactions is investigated. We find the spinodal is associated with the zeros of the partition function in four-dimensional complex temperature/magnetic field space. The zeros approach the real temperature/magnetic field plane as the range of interaction increases.Comment: 20 pages, 9 figures, accepted to PR

"Exhaustion" Physics in the Periodic Anderson Model using Iterated Perturbation Theory

We discuss the "exhaustion" problem in the context of the Periodic Anderson Model using Iterated Perturbation Theory(IPT) within the Dynamical Mean Field Theory. We find that, despite its limitations, IPT captures the exhaustion physics, which manifests itself as a dramatic, strongly energy dependent suppression of the effective Anderson impurity problem. As a consequence, low energy scales in the lattice case are strongly suppressed compared to the "Kondo scale" in the single-impurity picture. The IPT results are in qualitative agreement with recent Quantum Monte Carlo results for the same problem.Comment: 13 preprint pages including 1 table and 4 eps figures, replaced by revised version, accepted for publication in Europhysics Letters, added references and conten

Clusters and Fluctuations at Mean-Field Critical Points and Spinodals

We show that the structure of the fluctuations close to spinodals and mean-field critical points is qualitatively different than the structure close to non-mean-field critical points. This difference has important implications for many areas including the formation of glasses in supercooled liquids. In particular, the divergence of the measured static structure function in near-mean-field systems close to the glass transition is suppressed relative to the mean-field prediction in systems for which a spatial symmetry is broken.Comment: 5 pages, 1 figur

The instability of Alexander-McTague crystals and its implication for nucleation

We show that the argument of Alexander and McTague, that the bcc crystalline structure is favored in those crystallization processes where the first order character is not too pronounced, is not correct. We find that any solution that satisfies the Alexander-McTague condition is not stable. We investigate the implication of this result for nucleation near the pseudo- spinodal in near-meanfield systems.Comment: 20 pages, 0 figures, submitted to Physical Review

Exact Criterion for Determining Clustering vs. Reentrant Melting Behavior for Bounded Interaction Potentials

We examine in full generality the phase behavior of systems whose constituent particles interact by means of potentials which do not diverge at the origin, are free of attractive parts and decay fast enough to zero as the interparticle separation r goes to infinity. By employing a mean field-density functional theory which is shown to become exact at high temperatures and/or densities, we establish a criterion which determines whether a given system will freeze at all temperatures or it will display reentrant melting and an upper freezing temperature.Comment: 5 pages, 3 figures, submitted to PRL on March 29, 2000 New version: 10 pages, 9 figures, forwarded to PRE on October 16, 200

Theory of One-Channel vs. Multi-Channel Kondo Effects for Ce3+^{3+} Impurities

We introduce a model for Ce$^{3+}$ impurities in cubic metals which exhibits competition between the Fermi-liquid fixed point of the single channel Kondo model and the non-Fermi-liquid fixed point of the two- and three-channel Kondo models. Using the non-crossing approximation and scaling theory, we find: (i) A possible three-channel Kondo effect between the one- and two-channel regimes in parameter space. (ii) The sign of the thermopower is a fixed point diagnostic. (iii) Our results will likely survive the introduction of additional $f^2$ and conduction states. We apply this model to interpret the non-Fermi liquid alloy La$_{1-x}$Ce$_x$Cu$_{2.2}$Si$_2$.Comment: 13 pages, Revtex, To appear in Phys. Rev. Let