5,481 research outputs found
Building CMS Pixel Barrel Detectur Modules
For the barrel part of the CMS pixel tracker about 800 silicon pixel detector
modules are required. The modules are bump bonded, assembled and tested at the
Paul Scherrer Institute. This article describes the experience acquired during
the assembly of the first ~200 modules.Comment: 5 pages, 7 figures, Vertex200
Prospects of high temperature ferromagnetism in (Ga,Mn)As semiconductors
We report on a comprehensive combined experimental and theoretical study of
Curie temperature trends in (Ga,Mn)As ferromagnetic semiconductors. Broad
agreement between theoretical expectations and measured data allows us to
conclude that T_c in high-quality metallic samples increases linearly with the
number of uncompensated local moments on Mn_Ga acceptors, with no sign of
saturation. Room temperature ferromagnetism is expected for a 10% concentration
of these local moments. Our magnetotransport and magnetization data are
consistnent with the picture in which Mn impurities incorporated during growth
at interstitial Mn_I positions act as double-donors and compensate neighboring
Mn_Ga local moments because of strong near-neighbor Mn_Ga-Mn_I
antiferromagnetic coupling. These defects can be efficiently removed by
post-growth annealing. Our analysis suggests that there is no fundamental
obstacle to substitutional Mn_Ga doping in high-quality materials beyond our
current maximum level of 6.2%, although this achievement will require further
advances in growth condition control. Modest charge compensation does not limit
the maximum Curie temperature possible in ferromagnetic semiconductors based on
(Ga,Mn)As.Comment: 13 pages, 12 figures, submitted to Phys. Rev.
CMS Barrel Pixel Detector Overview
The pixel detector is the innermost tracking device of the CMS experiment at
the LHC. It is built from two independent sub devices, the pixel barrel and the
end disks. The barrel consists of three concentric layers around the beam pipe
with mean radii of 4.4, 7.3 and 10.2 cm. There are two end disks on each side
of the interaction point at 34.5 cm and 46.5 cm. This article gives an overview
of the pixel barrel detector, its mechanical support structure, electronics
components, services and its expected performance.Comment: Proceedings of Vertex06, 15th International Workshop on Vertex
Detector
Identical Bands in Superdeformed Nuclei: A Relativistic Description
Relativistic Mean Field Theory in the rotating frame is used to describe
superdeformed nuclei. Nuclear currents and the resulting spatial components of
the vector meson fields are fully taken into account. Identical bands in
neighboring Rare Earth nuclei are investigated and excellent agreement with
recent experimental data is observed.Comment: 11 pages (Latex) and 4 figures (available upon request)
TUM-ITP-Ko93/
Kondo Correlations and the Fano Effect in Closed AB-Interferometers
We study the Fano-Kondo effect in a closed Aharonov-Bohm (AB) interferometer
which contains a single-level quantum dot and predict a frequency doubling of
the AB oscillations as a signature of Kondo-correlated states. Using Keldysh
formalism, Friedel sum rule and Numerical Renormalization Group, we calculate
the exact zero-temperature linear conductance as a function of AB phase
and level position . In the unitary limit, reaches
its maximum at . We find a Fano-suppressed Kondo plateau
for similar to recent experiments.Comment: 4 pages, 4 eps figure
Sequential and co-tunneling behavior in the temperature-dependent thermopower of few-electron quantum dots
We have studied the temperature dependent thermopower of gate-defined,
lateral quantum dots in the Coulomb blockade regime using an electron heating
technique. The line shape of the thermopower oscillations depends strongly on
the contributing tunneling processes. Between 1.5 K and 40 mK a crossover from
a pure sawtooth- to an intermitted sawtooth-like line shape is observed. The
latter is attributed to the increasing dominance of cotunneling processes in
the Coulomb blockade regime at low temperatures.Comment: 4 pages, 4 figures, submitted to Phys. Rev.
MUBs inequivalence and affine planes
There are fairly large families of unitarily inequivalent complete sets of
N+1 mutually unbiased bases (MUBs) in C^N for various prime powers N. The
number of such sets is not bounded above by any polynomial as a function of N.
While it is standard that there is a superficial similarity between complete
sets of MUBs and finite affine planes, there is an intimate relationship
between these large families and affine planes. This note briefly summarizes
"old" results that do not appear to be well-known concerning known families of
complete sets of MUBs and their associated planes.Comment: This is the version of this paper appearing in J. Mathematical
Physics 53, 032204 (2012) except for format changes due to the journal's
style policie
Ferromagnetism in Diluted Magnetic Semiconductor Heterojunction Systems
Diluted magnetic semiconductors (DMSs), in which magnetic elements are
substituted for a small fraction of host elements in a semiconductor lattice,
can become ferromagnetic when doped. In this article we discuss the physics of
DMS ferromagnetism in systems with semiconductor heterojunctions. We focus on
the mechanism that cause magnetic and magnetoresistive properties to depend on
doping profiles, defect distributions, gate voltage, and other system
parameters that can in principle be engineered to yield desired results.Comment: 12 pages, 7 figures, review, special issue of Semicon. Sci. Technol.
on semiconductor spintronic
Aharonov-Bohm interferometry with quantum dots: scattering approach versus tunneling picture
We address the question of how to model electron transport through closed
Aharonov-Bohm interferometers which contain quantum dots. By explicitly
studying interferometers with one and two quantum dots, we establish the
connection between a tunneling-Hamiltonian formulation on the one hand and a
scattering-matrix approach on the other hand. We prove that, under certain
circumstances, both approaches are equivalent, i.e., both types of models can
describe the same experimental setups. Furthermore, we analyze how the
interplay of the Aharonov-Bohm phase and the orbital phase associated with the
lengths of the interferometers' arms affect transport properties.Comment: 8 pages, 8 figures, published versio
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