3,439 research outputs found
Diagrammatic theory of the Anderson impurity model with finite Coulomb interaction
We have developed a self-consistent conserving pseudo particle approximation
for the Anderson impurity model with finite Coulomb interaction, derivable from
a Luttinger Ward functional. It contains an infinite series of skeleton
diagrams built out of fully renormalized Green's functions. The choice of
diagrams is motivated by the Schrieffer Wolff transformation which shows that
singly and doubly occupied states should appear in all bare diagrams
symmetrically. Our numerical results for are in excellent agreement with
the exact values known from the Bethe ansatz solution. The low energy physics
of non-Fermi liquid Anderson impurity systems is correctly described while the
present approximation fails to describe Fermi liquid systems, since some
important coherent spin flip and charge transfer processes are not yet
included. It is believed that CTMA (Conserving T-matrix approximation) diagrams
will recover also Fermi liquid behavior for Anderson models with finite Coulomb
interaction as they do for infinite Coulomb interaction.Comment: 4 pages, 2 figures, presented at the NATO Advanced Research Workshop
on "Size Dependent MAgnetic Scattering", Pecs, Hungary, May 28 - June 1, 200
Nonequilibrium Transport through a Kondo Dot: Decoherence Effects
We investigate the effects of voltage induced spin-relaxation in a quantum
dot in the Kondo regime. Using nonequilibrium perturbation theory, we determine
the joint effect of self-energy and vertex corrections to the conduction
electron T-matrix in the limit of transport voltage much larger than
temperature. The logarithmic divergences, developing near the different
chemical potentials of the leads, are found to be cut off by spin-relaxation
rates, implying that the nonequilibrium Kondo-problem remains at weak coupling
as long as voltage is much larger than the Kondo temperature.Comment: 16 pages, 4 figure
Non Equilibrium Noise as a Probe of the Kondo Effect in Mesoscopic Wires
We study the non-equilibrium noise in mesoscopic diffusive wires hosting
magnetic impurities. We find that the shot-noise to current ratio develops a
peak at intermediate source-drain biases of the order of the Kondo temperature.
The enhanced impurity contribution at intermediate biases is also manifested in
the effective distribution. The predicted peak represents increased inelastic
scattering rate at the non-equilibrium Kondo crossover.Comment: 4+ pages, 4 figures, published versio
Performance of a First-Level Muon Trigger with High Momentum Resolution Based on the ATLAS MDT Chambers for HL-LHC
Highly selective first-level triggers are essential to exploit the full
physics potential of the ATLAS experiment at High-Luminosity LHC (HL-LHC). The
concept for a new muon trigger stage using the precision monitored drift tube
(MDT) chambers to significantly improve the selectivity of the first-level muon
trigger is presented. It is based on fast track reconstruction in all three
layers of the existing MDT chambers, made possible by an extension of the
first-level trigger latency to six microseconds and a new MDT read-out
electronics required for the higher overall trigger rates at the HL-LHC. Data
from -collisions at is used to study the
minimal muon transverse momentum resolution that can be obtained using the MDT
precision chambers, and to estimate the resolution and efficiency of the
MDT-based trigger. A resolution of better than is found in all sectors
under study. With this resolution, a first-level trigger with a threshold of
becomes fully efficient for muons with a transverse momentum
above in the barrel, and above in the
end-cap region.Comment: 6 pages, 11 figures; conference proceedings for IEEE NSS & MIC
conference, San Diego, 201
Strong vs. Weak Coupling Duality and Coupling Dependence of the Kondo Temperature in the Two-Channel Kondo Model
We perform numerical renormalization group (NRG) as well as analytical
calculations for the two-channel Kondo model to obtain the dependence of the
Kondo temperature on the dimensionless (bare) spin exchange coupling
over the complete parameter range from to . We show that there
exists a duality between the regimes of small and large coupling. It is unique
for the two-channel model and enables a mapping between the strong and the weak
coupling cases via the identification , implying an
exponential dependence of on and , respectively, in the two
regimes. This agrees quantitatively with our NRG calculations where we extract
over the complete parameter range and obtain a non-monotonous
dependence, strongly peaked at the 2CK fixed point coupling . These
results may be relevant for resolving the long-standing puzzle within the 2CK
interpretation of certain random defect systems, why no broad distribution of
is observed in those systems.Comment: 6 pages, 3 figures; PRB published version, shortened, nomenclature
clarifie
Asymmetry effects on the phases of RKKY-coupled two-impurity Kondo systems
In a related work [arXiv:2106.07519] we have shown that in the two-impurity
Anderson (2iA) model with two hosts coupled by spin exchange in the most
symmetric case there are either two phase transitions or none. The phases
comprise the conventional Kondo and RKKY regimes and a novel one, interpreted
as a Kondo-stabilized, metallic quantum spin liquid (QSL). Here we analyze how
various types of asymmetry affect this picture. We demonstrate that the
transitions are robust against the coupling and particle-hole asymmetries,
provided charge transfer is forbidden. This holds true despite the scattering
phase shift at each impurity taking non-universal values. Finally, for an
extended model including charge transfer between the hosts and a small Coulomb
interaction at the host sites directly coupled to impurities, we show that the
presence of charge transfer changes the phase transitions into crossovers.
Provided the inter-host hopping is sufficiently small, this leads to
qualitatively the same physics at non-zero temperature. The relevance of this
model for rare-earth atoms in a metallic host is discussed and potential
experimental setups for observing our findings are proposed.Comment: 13 pages, 12 figure
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