16 research outputs found
Stability of spin droplets in realistic quantum Hall devices
We study the formation and characteristics of "spin droplets",i.e., compact
spin-polarized configurations in the highest occupied Landau level, in an
etched quantum Hall device at filling factors . The confining
potential for electrons is obtained with self-consistent electrostatic
calculations on a GaAs/AlGaAs heterostructure with experimental system
parameters. Real-space spin-density-functional calculations for electrons
confined in the obtained potential show the appearance of stable spin droplets
at . The qualitative features of the spin droplet are similar to
those in idealized (parabolic) quantum-dot systems. The universal stability of
the state against geometric deformations underline the applicability of spin
droplets in, e.g., spin-transport through quantum point contacts.Comment: 11 pages, 6 figure
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
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
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 quantized Hall (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 nonlinear 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, but 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 QH conditions
A REVIEW OF GRID TECHNOLOGIES AND APPLICATION POSSIBILITIES IN
Grid technology emerged from the need for huge computational power and data storage capabilities for a range of applications such as high energy physics. The main objective of the Grid project is to combine the computation power of distributed resources such as computers, networks, databases and scientific instruments, across research centers over the country or even the globe. In such an arrangement, individual users can reach and share the desired resources from any point in the system. This system allows the researchers to share their experience and to process their data in a very short time. In this paper along with the basics of the Grid technology, the present infrastructure and possible applications in Turkey, especially in high energy physics, as in Atlas experiment, are investigated. Also future possibilities are discussed in this context