35,608 research outputs found
Thermal dependence of the zero-bias conductance through a nanostructure
We show that the conductance of a quantum wire side-coupled to a quantum dot,
with a gate potential favoring the formation of a dot magnetic moment, is a
universal function of the temperature. Universality prevails even if the
currents through the dot and the wire interfere. We apply this result to the
experimental data of Sato et al.[Phys. Rev. Lett. 95, 066801 (2005)].Comment: 6 pages, 3 figures. More detailed presentation, and updated
references. Final version
Quantum Dissipation in a Neutrino System Propagating in Vacuum and in Matter
Considering the neutrino state like an open quantum system, we analyze its
propagation in vacuum or in matter. After defining what can be called
decoherence and relaxation effects, we show that in general the probabilities
in vacuum and in constant matter can be written in a similar way, which is not
an obvious result in this approach. From this result, we analyze the situation
where neutrinos evolution satisfies the adiabatic limit and use this formalim
to study solar neutrinos. We show that the decoherence effect may not be
bounded by the solar neutrino data and review some results in the literature.
We discuss the current results where solar neutrinos were used to put bounds on
decoherence effects through a model-dependent approach. We conclude explaining
how and why this models are not general and we reinterpret these constraints.Comment: new version: title was changend and was added a table. To appear at
Nucl. Physic.
Universal zero-bias conductance through a quantum wire side-coupled to a quantum dot
A numerical renormalization-group study of the conductance through a quantum
wire side-coupled to a quantum dot is reported. The temperature and the
dot-energy dependence of the conductance are examined in the light of a
recently derived linear mapping between the Kondo-regime temperature-dependent
conductance and the universal function describing the conductance for the
symmetric Anderson model of a quantum wire with an embedded quantum dot. Two
conduction paths, one traversing the wire, the other a bypass through the
quantum dot, are identified. A gate potential applied to the quantum wire is
shown to control the flow through the bypass. When the potential favors
transport through the wire, the conductance in the Kondo regime rises from
nearly zero at low temperatures to nearly ballistic at high temperatures. When
it favors the dot, the pattern is reversed: the conductance decays from nearly
ballistic to nearly zero. When the fluxes through the two paths are comparable,
the conductance is nearly temperature-independent in the Kondo regime, and a
Fano antiresonance in the fixed-temperature plot of the conductance as a
function of the dot energy signals interference. Throughout the Kondo regime
and, at low temperatures, even in the mixed-valence regime, the numerical data
are in excellent agreement with the universal mapping.Comment: 12 pages, with 9 figures. Submitted to PR
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