785 research outputs found
Kondo screening cloud in a one dimensional wire: Numerical renormalization group study
We study the Kondo model --a magnetic impurity coupled to a one dimensional
wire via exchange coupling-- by using Wilson's numerical renormalization group
(NRG) technique. By applying an approach similar to which was used to compute
the two impurity problem we managed to improve the bad spatial resolution of
the numerical renormalization group method. In this way we have calculated the
impurity spin - conduction electron spin correlation function which is a
measure of the Kondo compensation cloud whose existence has been a long
standing problem in solid state physics. We also present results on the
temperature dependence of the Kondo correlations.Comment: published versio
Perturbative treatment of the multichannel interacting resonant level model in steady state non-equilibrium
We consider the steady state non-equilibrium physics of the multichannel
interacting resonant level model in the weak coupling regime. By using the
scattering state method we show in agreement with the rate equations that the
negative differential conductance at large enough voltages is due to the
renormalization of the hopping amplitude thus of the vertex.Comment: 3+ pages, 4 figure
Absorption and Emission in quantum dots: Fermi surface effects of Anderson excitons
Recent experiments measuring the emission of exciton recombination in a
self-organized single quantum dot (QD) have revealed that novel effects occur
when the wetting layer surrounding the QD becomes filled with electrons,
because the resulting Fermi sea can hybridize with the local electron levels on
the dot. Motivated by these experiments, we study an extended Anderson model,
which describes a local conduction band level coupled to a Fermi sea, but also
includes a local valence band level. We are interested, in particular, on how
many-body correlations resulting from the presence of the Fermi sea affect the
absorption and emission spectra. Using Wilson's numerical renormalization group
method, we calculate the zero-temperature absorption (emission) spectrum of a
QD which starts from (ends up in) a strongly correlated Kondo ground state. We
predict two features: Firstly, we find that the spectrum shows a power law
divergence close to the threshold, with an exponent that can be understood by
analogy to the well-known X-ray edge absorption problem. Secondly, the
threshold energy - below which no photon is absorbed (above which no
photon is emitted) - shows a marked, monotonic shift as a function of the
exciton binding energy Comment: 10 pages, 9 figure
Quantum Magnetic Impurities in Magnetically Ordered Systems
We discuss the problem of a spin 1/2 impurity immersed in a spin S
magnetically ordered background. We show that the problem maps onto a
generalization of the dissipative two level system (DTLS) with two independent
heat baths, associated with the Goldstone modes of the magnet, that couple to
different components of the impurity spin operator. Using analytical
perturbative renormalization group (RG) methods and accurate numerical
renormalization group (NRG) we show that contrary to other dissipative models
there is quantum frustration of decoherence and quasi-scaling even in the
strong coupling regime. We make predictions for the behavior of the impurity
magnetic susceptibility that can be measured in nuclear magnetic resonance
(NMR) experiments. Our results may also have relevance to quantum computation.Comment: 4 pages, 3 figure
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