5,286 research outputs found
Simple model for scanning tunneling spectroscopy of noble metal surfaces with adsorbed Kondo impurities
A simple model is introduced to describe conductance measurements between a
scanning tunneling microscope (STM) tip and a noble metal surface with adsorbed
transition metal atoms which display the Kondo effect. The model assumes a
realistic parameterization of the potential created by the surface and a
d3z2-r2 orbital for the description of the adsorbate. Fano lineshapes
associated with the Kondo resonance are found to be sensitive to details of the
adsorbate-substrate interaction. For instance, bringing the adsorbate closer to
the surface leads to more asymmetric lineshapes while their dependence on the
tip distance is weak. We find that it is important to use a realistic surface
potential, to properly include the tunnelling matrix elements to the tip and to
use substrate states which are orthogonal to the adsorbate and tip states. An
application of our model to Co adsorbed on Cu explains the difference in the
lineshapes observed between Cu(100) and Cu(111) surfaces.Comment: 11 pages, 8 eps figure
Coherent properties of nano-electromechanical systems
We study the properties of a nano-electromechanical system in the coherent
regime, where the electronic and vibrational time scales are of the same order.
Employing a master equation approach, we obtain the stationary reduced density
matrix retaining the coherences between vibrational states. Depending on the
system parameters, two regimes are identified, characterized by either () an
{\em effective} thermal state with a temperature {\em lower} than that of the
environment or () strong coherent effects. A marked cooling of the
vibrational degree of freedom is observed with a suppression of the vibron Fano
factor down to sub-Poissonian values and a reduction of the position and
momentum quadratures.Comment: 12 pages, 11 figure
Fano resonances and decoherence in transport through quantum dots
A tunable microwave scattering device is presented which allows the
controlled variation of Fano line shape parameters in transmission through
quantum billiards. We observe a non-monotonic evolution of resonance parameters
that is explained in terms of interacting resonances. The dissipation of
radiation in the cavity walls leads to decoherence and thus to a modification
of the Fano profile. We show that the imaginary part of the complex Fano
q-parameter allows to determine the absorption constant of the cavity. Our
theoretical results demonstrate further that the two decohering mechanisms,
dephasing and dissipation, are equivalent in terms of their effect on the
evolution of Fano resonance lineshapes.Comment: 9 pages, 7 figures, submitted to Physica E (conference proceedings
Shot Noise of Spin-Decohering Transport in Spin-Orbit Coupled Nanostructures
We generalize the scattering theory of quantum shot noise to include the full
spin-density matrix of electrons injected from a spin-filtering or
ferromagnetic electrode into a quantum-coherent nanostructure governed by
various spin-dependent interactions. This formalism yields the spin-resolved
shot noise power for different experimental measurement setups--with
ferromagnetic source and ferromagnetic or normal drain electrodes--whose
evaluation for the diffusive multichannel quantum wires with the Rashba (SO)
spin-orbit coupling shows how spin decoherence and dephasing lead to
substantial enhancement of charge current fluctuations (characterized by Fano
factors ). However, these processes and the corresponding shot noise
increase are suppressed in narrow wires, so that charge transport experiments
measuring the Fano factor in a
ferromagnet/SO-coupled-wire/paramagnet setup also quantify the degree of
phase-coherence of transported spin--we predict a one-to-one correspondence
between the magnitude of the spin polarization vector and .Comment: 8 pages, 3 figure; enhanced with 2 new figure
Configuration interaction in delta-doped heterostructures
We analyze the tunnel coupling between an impurity state located in a
-layer and the 2D delocalized states in the quantum well (QW) located
at a few nanometers from the -- layer. The problem is formulated in
terms of Anderson-Fano model as configuration interaction between the carrier
bound state at the impurity and the continuum of delocalized states in the QW.
An effect of this interaction on the interband optical transitions in the QW is
analyzed. The results are discussed regarding the series of experiments on the
GaAs structures with a -Mn layer.Comment: arXiv admin note: substantial text overlap with arXiv:1111.089
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