94 research outputs found
Microscopic theory of the activated behavior of the quantized Hall effect
The thermally activated behavior of the gate defined narrow Hall bars is
studied by analyzing the existence of the incompressible strips within a
Hartree-type approximation. We perform self-consistent calculations considering
the linear response regime, supported by a local conductivity model. We
investigate the variation of the activation energy depending on the width of
samples in the range of . We show that the largest
activation energy of high-mobility narrow samples, is at the low field edge of
Hall filling factor 2 plateau (exceeding half of the cyclotron energy), whereas
for relatively wide samples the higher activation energy is obtained at the
high field edge of Hall plateau. In contrast to the single-particle theories
based on the localization of electronic states, we found that the activation
energy is almost independent of the properties of the density of states.Comment: 8 pages, 4 figure
Quantum Hall Resistance Overshoot in 2-Dimensional Electron Gases - Theory and Experiment
We present a systematical experimental investigation of an unusual transport
phenomenon observed in two dimensional electron gases in Si/SiGe
heterostructures under integer quantum Hall effect (IQHE) conditions. This
phenomenon emerges under specific experimental conditions and in different
material systems. It is commonly referred to as Hall resistance overshoot,
however, lacks a consistent explanation so far. Based on our experimental
findings we are able to develop a model that accounts for all of our
observations in the framework of a screening theory for the IQHE. Within this
model the origin of the overshoot is attributed to a transport regime where
current is confined to co-existing evanescent incompressible strips of
different filling factors.Comment: 26 pages, 10 figure
Interaction mediated asymmetries of the quantized Hall effect
Experimental and theoretical investigations on the integer quantized Hall
effect in gate defined narrow Hall bars are presented. At low electron mobility
the classical (high temperature) Hall resistance line RH(B) cuts through the
center of all Hall plateaus. In contrast, for our high mobility samples the
intersection point, at even filling factors \nu = 2; 4 ..., is clearly shifted
towards larger magnetic fields B. This asymmetry is in good agreement with
predictions of the screening theory, i. e. taking Coulomb interaction into
account. The observed effect is directly related to the formation of
incompressible strips in the Hall bar. The spin-split plateau at \nu= 1 is
found to be almost symmetric regardless of the mobility. We explain this within
the so-called effective g-model.Comment: 4 pages, 3 figure
Theoretical investigation of InAs/GaSb type-II pin superlattice infrared detector in the mid wavelength infrared range
In this study, we present the theoretical investigation of type-II InAs/GaSb superlattice p-i-n detector. Kronig-Penney and envelope function approximation is used to calculate band gap energy and superlattice minibands. Variational method is also used to calculate exciton binding energies. Our results show that carriers overlap increases at GaSb/InAs interface on the higher energy side while it decreases at InAs/GaSb interface on the lower energy side with increasing reverse bias due to shifting the hole wavefunction toward to the GaSb/InAs interface decisively. Binding energies increase with increasing electric field due to overall overlap of electron and hole wave functions at the both interfaces in contrast with type I superlattices. This predicts that optical absorption is enhanced with increasing electric field. © 2013 American Institute of Physics
The visibility of IQHE at sharp edges: Experimental proposals based on interactions and edge electrostatics
The influence of the incompressible strips on the integer quantized Hall
effect (IQHE) is investigated, considering a cleaved-edge overgrown (CEO)
sample as an experimentally realizable sharp edge system. We propose a set of
experiments to clarify the distinction between the large-sample limit when bulk
disorder defines the IQHE plateau width and the small-sample limit smaller than
the disorder correlation length, when self-consistent edge electrostatics
define the IQHE plateau width. The large-sample or bulk QH regime is described
by the usual localization picture, whereas the small-sample or edge regime is
discussed within the compressible/incompressible strips picture, known as the
screening theory of QH edges. Utilizing the unusually sharp edge profiles of
the CEO samples, a Hall bar design is proposed to manipulate the edge potential
profile from smooth to extremely sharp. By making use of a side-gate
perpendicular to the two dimensional electron system, it is shown that the
plateau widths can be changed or even eliminated altogether. Hence, the
visibility of IQHE is strongly influenced when adjusting the edge potential
profile and/or changing the dc current direction under high currents in the
non-linear transport regime. As a second investigation, we consider two
different types of ohmic contacts, namely highly transmitting (ideal) and
highly reflecting (non-ideal) contacts. We show that if the injection contacts
are non-ideal, however still ohmic, it is possible to measure directly the
non-quantized transport taking place at the bulk of the CEO samples. The
results of the experiments we propose will clarify the influence of the edge
potential profile and the quality of the contacts, under quantized Hall
conditions.Comment: Substantially revised version of manuscript arXiv:0906.3796v1,
including new figures et
Photoionization of donor impurities in quantum wires in a magnetic field
Using a variational approach, we have calculated the impurity position dependence of the photoionization cross-section and the binding energy of a hydrogenic donor impurity in a quantum well wire in the presence of the magnetic field as a function of the photon energy. Our calculations have revealed the dependence of the photoionization cross-section and the impurity binding on the applied magnetic field, the size of the wire and the impurity position
The effects of temperature and hydrostatic pressure on the photoionization cross-section and binding energy of shallow donor impurities in quantum dots
Using a variational approach we have calculated the hydrostatic pressure and temperature effects on the donor impurity related photoionization cross-section and impurity binding in GaAs/GaAlAs quantum dots Our calculations have revealed the dependence of the photoionizaton cross-section and the impurity binding on temperature and hydrostatic pressure (C) 2010 Elsevier Ltd All rights reserve
Photoionization cross-section and binding energy of shallow donor impurities in Ga1-xInxNyAs1-y/GaAs quantum wires
We have investigated the effects of the nitrogen and indium concentrations on the photoionization crosssection and binding energy of shallow donor impurities in Ga1-xInxNyAs1-y/GaAs quantum wires. The numerical calculations are performed in the effective mass approximation, using a variational method. We observe that incorporation of small amounts of nitrogen and indium leads to significant changes of the photoionization cross-section and binding energy. (C) 2011 Elsevier Ltd. All rights reserved
The effect of hydrostatic pressure on the photoionization cross-section and binding energy of impurities in quantum-well wire under the electric field
Using a variational approach, we have calculated the hydrostatic pressure and electric field effects on the donor-impurity related photoionization cross-section and impurity binding energy in GaAs/GaAlAs quantum well-wires. Both the results of impurity binding energy as a function of the impurity position and photoionization cross-section for a hydrogenic donor impurity placed at the center of the quantum well-wire as a function of the normalized photon energy in the quantum well-wire under the hydrostatic pressure and electric field which are applied to the z-direction for two different wire dimensions are presented. (c) 2005 Elsevier B.V. All rights reserved
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