18,193 research outputs found
Realization of Strong Coupling Fixed Point in Multilevel Kondo Models
Impurity four- and six-level Kondo model, in which an ion is tunneling among
four- and six-stable points and interacting with surrounding conduction
electrons, are investigated by using the perturbative and numerical
renormalization group methods. It is shown that purely orbital Kondo effects
occur at low temperatures in these systems which are direct generalizations of
the Kondo effect in the so-called two-level system. This result offers a good
explanation for the enhanced and magnetically robust Sommerfeld coefficient
observed in SmOs_4Sb_12 and some other filled-skutterudites.Comment: 3 pages, 3 figures, for proceedings of ASR-WYP-2005. To be published
in Journal of Physical Society Japan supplemen
Future of Ultraviolet Astronomy Based on Six Years of IUE Research
Physical insights into the various astronomical objects which were studied using the International Ultraviolet Explorer (IUE) satellite. Topics covered included galaxies, cool stars, hot stars, close binaries, variable stars, the interstellar medium, the solar system, and IUE follow-on missions
Superconductivity Driven by the Interband Coulomb Interaction and Implications for the Superconducting Mechanism of MgB2
Superconducting mechanism mediated by interband exchange Coulomb repulsion is
examined in an extended two-band Hubbard models with a wide band crossing the
Fermi level and coexisting with a narrower band located at moderately lower
energy. We apply newly developed path-integral renormalization group method to
reliably calculate pairing correlations. The correlation shows marked
enhancement at moderate amplitudes of the exchange Coulomb repulsion taken
smaller than the on-site repulsion for the narrower band. The pairing symmetry
is s-wave while it has unconventional phases with the opposite sign between the
order parameters on the two bands, in agreement with the mean-field prediction.
Since the band structure of recently discovered superconductor MgB shares
basic similarities with our model, we propose that the present results provide
a relevant clue for the understanding of the superconducting mechanism in
MgB as well as in this class of multi-band materials with good metallic
conduction in the normal state.Comment: 4pages, 2figure
A new approach to axial coupling constants in the QCD sum rule
We derive new QCD sum rules for the axial coupling constants by considering
two-point correlation functions of the axial-vector currents in a one nucleon
state. The QCD sum rules tell us that the axial coupling constants are
expressed by nucleon matrix elements of quark and gluon operators which are
related to the sigma terms and the moments of parton distribution functions.
The results for the iso-vector axial coupling constants and the 8th component
of the SU(3) octet are in good agreement with experiment.Comment: 10 pages, 1 figure include
Thermodynamic properties of Bi2Sr2CaCu2O8 calculated from the electronic dispersion
The electronic dispersion for Bi2Sr2CaCu2O(8+d) has been determined from
angle-resolved photoelectron spectroscopy (ARPES). From this dispersion we
calculate the entropy and superfluid density. Even with no adjustable
parameters we obtain an exceptional match with experimental data across the
entire phase diagram, thus indirectly confirming both the ARPES and
thermodynamic data. The van Hove singularity is crossed in the overdoped region
giving a distinctive linear-in-T temperature dependence in the superfluid
density there.Comment: 5 pages, 4 figures, submitted to Physical Review Letter
Growth states of catalytic reaction networks exhibiting energy metabolism
All cells derive nutrition by absorbing some chemical and energy resources
from the environment; these resources are used by the cells to reproduce the
chemicals within them, which in turn leads to an increase in their volume. In
this study, we introduce a protocell model exhibiting catalytic reaction
dynamics, energy metabolism, and cell growth. Results of extensive simulations
of this model show the existence of four phases with regard to the rates of
both the influx of resources and the cell growth. These phases include an
active phase with high influx and high growth rates, an inefficient phase with
high influx but low growth rates, a quasi-static phase with low influx and low
growth rates, and a death phase with negative growth rate. A mean field model
well explains the transition among these phases as bifurcations. The
statistical distribution of the active phase is characterized by a power law
and that of the inefficient phase is characterized by a nearly equilibrium
distribution. We also discuss the relevance of the results of this study to
distinct states in the existing cells.Comment: 21 pages, 5 figure
Berry's phase contribution to the anomalous Hall effect of gadolinium
When conduction electrons are forced to follow the local spin texture, the
resulting Berry phase can induce an anomalous Hall effect (AHE). In gadolinium,
as in double-exchange magnets, the exchange interaction is mediated by the
conduction electrons and the AHE may therefore resemble that of chromium
dioxide and other metallic double-exchange ferromagnets. The Hall resistivity,
magnetoresistance, and magnetization of single crystal gadolinium were measured
in fields up to 30 T. Measurements between 2 K and 400 K are consistent with
previously reported data. A scaling analysis for the Hall resistivity as a
function of the magnetization suggests the presence of a Berry's-phase
contribution to the anomalous Hall effect.Comment: 6 pages, 7 figures, submitted to Phys. Rev.
Kondo Effect in a Quantum Antidot
We report Kondo-like behaviour in a quantum antidot (a submicron depleted
region in a two-dimensional electron gas) in the quantum-Hall regime. When both
spin branches of the lowest Landau level encircle the antidot in a magnetic
field ( T), extra resonances occur between extended edge states via
antidot bound states when tunnelling is Coulomb blockaded. These resonances
appear only in alternating Coulomb-blockaded regions, and become suppressed
when the temperature or source-drain bias is raised. Although the exact
mechanism is unknown, we believe that Kondo-like correlated tunnelling arises
from skyrmion-type edge reconstruction. This observation demonstrates the
generality of the Kondo phenomenon.Comment: 9 pages, 3 figures (Fig.3 in colour), to appear in Phys. Rev. Let
Kondo resonances and anomalous gate dependence of electronic conduction in single-molecule transistors
We report Kondo resonances in the conduction of single-molecule transistors
based on transition metal coordination complexes. We find Kondo temperatures in
excess of 50 K, comparable to those in purely metallic systems. The observed
gate dependence of the Kondo temperature is inconsistent with observations in
semiconductor quantum dots and a simple single-dot-level model. We discuss
possible explanations of this effect, in light of electronic structure
calculations.Comment: 5 pages, four figures. Supplementary material at
http://www.ruf.rice.edu/~natelson/publications.htm
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