51 research outputs found
Spatial distribution of local tunneling conductivity due to interference and Coulomb interaction effects for deep and shallow impurities on semiconductor surfaces
Spatial distribution of local tunneling conductivity was investigated for
deep and shallow impurities on semiconductor surfaces. Non-equilibrium Coulomb
interaction and interference effects were taken into account and analyzed
theoretically with the help of Keldysh formalism. Two models were investigated:
mean field self-consistent approach for shallow impurity state and Hubbard-{I}
model for deep impurity state. We have found that not only above the impurity
but also at the distances comparable to the lattice period both effects
interference between direct and resonant tunneling channels and on-site Coulomb
repulsion of localized electrons strongly modifies form of tunneling
conductivity measured by the scanning tunneling microscopy/spectroscopy
(STM/STS).Comment: 5 pages, 3 figure
All-electrical control of single ion spins in a semiconductor
We propose a method for all-electrical initialization, control and readout of
the spin of single ions substituted into a semiconductor. Mn ions in GaAs form
a natural example. In the ion's ground state the Mn core spin magnetic moment
locks antiparallel to the spin and orbital magnetic moment of a bound valence
hole from the GaAs host. Direct electrical manipulation of the ion spin is
possible because electric fields manipulate the orbital wave function of the
hole, and through the spin-orbit coupling the spin is reoriented as well.
Coupling two or more ion spins can be achieved using electrical gates to
control the size of the valence hole wave function near the semiconductor
surface. This proposal for coherent manipulation of individual ionic spins and
controlled coupling of ionic spins via electrical gates alone may find
applications in extremely high density information storage and in scalable
coherent or quantum information processing.Comment: 5 pages, 3 figure
The influence of localized states charging on 1/f^{\alpha} tunneling current noise spectrum
We report the results of theoretical investigations of low frequency
tunneling current noise spectra component (1/f^{\alpha}). Localized states of
individual impurity atoms play the key role in low frequency tunneling current
noise formation. It is found that switching "on" and "off" of Coulomb
interaction of conduction electrons with one or two charged localized states
results in power law singularity of low-frequency tunneling current noise
spectrum 1/f^{\alpha}. Power law exponent in different low frequency ranges
depends on the relative values of Coulomb interaction of conduction electrons
with different charged impurities.Comment: 7 pages, 5 figure
Tuning of tunneling current noise spectra singularities by localized states charging
We report the results of theoretical investigations of tunneling current
noise spectra in a wide range of applied bias voltage. Localized states of
individual impurity atoms play an important role in tunneling current noise
formation. It was found that switching "on" and "off" of Coulomb interaction of
conduction electrons with two charged localized states results in power law
singularity of low-frequency tunneling current noise spectrum ()
and also results on high frequency component of tunneling current spectra
(singular peaks appear).Comment: 7 pages, 4 figure
Scanning tunneling microscopy and spectroscopy at low temperatures of the (110) surface of Te doped GaAs single crystals
We have performed voltage dependent imaging and spatially resolved
spectroscopy on the (110) surface of Te doped GaAs single crystals with a low
temperature scanning tunneling microscope (STM). A large fraction of the
observed defects are identified as Te dopant atoms which can be observed down
to the fifth subsurface layer. For negative sample voltages, the dopant atoms
are surrounded by Friedel charge density oscillations. Spatially resolved
spectroscopy above the dopant atoms and above defect free areas of the GaAs
(110) surface reveals the presence of conductance peaks inside the
semiconductor band gap. The appearance of the peaks can be linked to charges
residing on states which are localized within the tunnel junction area. We show
that these localized states can be present on the doped GaAs surface as well as
at the STM tip apex.Comment: 8 pages, 8 figures, accepted for publication in PR
Coulomb singularity effects in tunnelling spectroscopy of individual impurities
Non-equilibrium Coulomb effects in resonant tunnelling processes through deep
impurity states are analyzed. It is shown that Coulomb vertex corrections to
the tunnelling transfer amplitude lead to a power-law singularity in current-
voltage characteristicsComment: 7 pages, 2 figure
The mechanism of hole carrier generation and the nature of pseudogap- and 60K-phases in YBCO
In the framework of the model assuming the formation of NUC on the pairs of
Cu ions in CuO plane the mechanism of hole carrier generation is
considered and the interpretation of pseudogap and 60 K-phases in
. is offered. The calculated dependences of hole
concentration in on doping and temperature
are found to be in a perfect quantitative agreement with experimental data. As
follows from the model the pseudogap has superconducting nature and arises at
temperature in small clusters uniting a number of
NUC's due to large fluctuations of NUC occupation. Here and
are the superconducting transition temperatures of infinite and finite
clusters of NUC's, correspondingly. The calculated and
dependences are in accordance with experiment. The area between
and corresponds to the area of fluctuations
where small clusters fluctuate between superconducting and normal states owing
to fluctuations of NUC occupation. The results may serve as important arguments
in favor of the proposed model of HTSC.Comment: 12 pages, 7 figure
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