7,198 research outputs found
Investigation of thin n-in-p planar pixel modules for the ATLAS upgrade
In view of the High Luminosity upgrade of the Large Hadron Collider (HL-LHC),
planned to start around 2023-2025, the ATLAS experiment will undergo a
replacement of the Inner Detector. A higher luminosity will imply higher
irradiation levels and hence will demand more ra- diation hardness especially
in the inner layers of the pixel system. The n-in-p silicon technology is a
promising candidate to instrument this region, also thanks to its
cost-effectiveness because it only requires a single sided processing in
contrast to the n-in-n pixel technology presently employed in the LHC
experiments. In addition, thin sensors were found to ensure radiation hardness
at high fluences. An overview is given of recent results obtained with not
irradiated and irradiated n-in-p planar pixel modules. The focus will be on
n-in-p planar pixel sensors with an active thickness of 100 and 150 um recently
produced at ADVACAM. To maximize the active area of the sensors, slim and
active edges are implemented. The performance of these modules is investigated
at beam tests and the results on edge efficiency will be shown
Effective T-odd P-even hadronic interactions from quark models
Tests of time reversal symmetry at low and medium energies may be analyzed in
the framework of effective hadronic interactions. Here, we consider the quark
structure of hadrons to make a connection to the more fundamental degrees of
freedom. It turns out that for P-even T-odd interactions hadronic matrix
elements evaluated in terms of quark models give rise to factors of 2 to 5.
Also, it is possible to relate the strength of the anomalous part of the
effective rho-type T-odd P-even tensor coupling to quark structure effects.Comment: 6 pages, 1 figure, RevTe
Investigating the Physical Origin of Unconventional Low-Energy Excitations and Pseudogap Phenomena in Cuprate Superconductors
We investigate the physical origin of unconventional low-energy excitations
in cuprate superconductors by considering the effect of coexisting competing
orders (CO) and superconductivity (SC) and of quantum fluctuations and other
bosonic modes on the low-energy charge excitation spectra. By incorporating
both SC and CO in the bare Green's function and quantum phase fluctuations in
the self-energy, we can consistently account for various empirical findings in
both the hole- and electron-type cuprates, including the excess subgap
quasiparticle density of states, ``dichotomy'' in the fluctuation-renormalized
quasiparticle spectral density in momentum space, and the occurrence and
magnitude of a low-energy pseudogap being dependent on the relative gap
strength of CO and SC. Comparing these calculated results with experiments of
ours and others, we suggest that there are two energy scales associated with
the pseudogap phenomena, with the high-energy pseudogap probably of magnetic
origin and the low-energy pseudogap associated with competing orders.Comment: 10 pages, 5 figures. Invited paper for the 2006 Taiwan International
Conference on Superconductivity. Correspondence author: Nai-Chang Yeh
(e-mail: [email protected]
Spin-polarized tunneling spectroscopic studies of the intrinsic heterogeneity and pseudogap phenomena in colossal magnetoresistive manganite La_{0.7}Ca_{0.3}MnO_{3}
Spatially resolved tunneling spectroscopic studies of colossal
magnetoresistive (CMR) manganite (LCMO) epitaxial
films on substrate are investigated as
functions of temperature, magnetic field and spin polarization by means of
scanning tunneling spectroscopy. Systematic surveys of the tunneling spectra
taken with Pt/Ir tips reveal spatial variations on the length scale of a few
hundred nanometers in the ferromagnetic state, which may be attributed to the
intrinsic heterogeneity of the manganites due to their tendency towards phase
separation. The electronic heterogeneity is found to decrease either with
increasing field at low temperatures or at temperatures above all magnetic
ordering temperatures. On the other hand, spectra taken with Cr-coated tips are
consistent with convoluted electronic properties of both LCMO and Cr. In
particular, for temperatures below the magnetic ordering temperatures of both
Cr and LCMO, the magnetic-field dependent tunneling spectra may be
quantitatively explained by the scenario of spin-polarized tunneling in a
spin-valve configuration. Moreover, a low-energy insulating energy gap eV commonly found in the tunneling conductance spectra of bulk metallic
LCMO at may be attributed to a surface ferromagnetic insulating (FI)
phase, as evidenced by its spin filtering effect at low temperatures and
vanishing gap value above the Curie temperature. Additionally, temperature
independent pseudogap (PG) phenomena existing primarily along the boundaries of
magnetic domains are observed in the zero-field tunneling spectra. The PG
becomes strongly suppressed by applied magnetic fields at low temperatures when
the tunneling spectra of LCMO become highly homogeneous. These findings suggest
that the occurrence PG is associated with the electronic heterogeneity of the
manganites.Comment: 15 pages, 15 figures. Published in Physical Review B. Corresponding
author: Nai-Chang Yeh (E-mail: [email protected]
An Integral Spectral Representation of the Propagator for the Wave Equation in the Kerr Geometry
We consider the scalar wave equation in the Kerr geometry for Cauchy data
which is smooth and compactly supported outside the event horizon. We derive an
integral representation which expresses the solution as a superposition of
solutions of the radial and angular ODEs which arise in the separation of
variables. In particular, we prove completeness of the solutions of the
separated ODEs.
This integral representation is a suitable starting point for a detailed
analysis of the long-time dynamics of scalar waves in the Kerr geometry.Comment: 41 pages, 4 figures, minor correction
Observation of vortices and hidden pseudogap from scanning tunneling spectroscopic studies of electron-doped cuprate superconductor
We present the first demonstration of vortices in an electron-type cuprate
superconductor, the highest (= 43 K) electron-type cuprate
. Our spatially resolved quasiparticle tunneling spectra
reveal a hidden low-energy pseudogap inside the vortex core and unconventional
spectral evolution with temperature and magnetic field. These results cannot be
easily explained by the scenario of pure superconductivity in the ground state
of high- superconductivity.Comment: 6 pages, 4 figures. Two new graphs have been added into Figure 2.
Accepted for publication in Europhysics Letters. Corresponding author:
Nai-Chang Yeh (E-mail: [email protected]
Investigations of solutions of Einstein's field equations close to lambda-Taub-NUT
We present investigations of a class of solutions of Einstein's field
equations close to the family of lambda-Taub-NUT spacetimes. The studies are
done using a numerical code introduced by the author elsewhere. One of the main
technical complication is due to the S3-topology of the Cauchy surfaces.
Complementing these numerical results with heuristic arguments, we are able to
yield some first insights into the strong cosmic censorship issue and the
conjectures by Belinskii, Khalatnikov, and Lifschitz in this class of
spacetimes. In particular, the current investigations suggest that strong
cosmic censorship holds in this class. We further identify open issues in our
current approach and point to future research projects.Comment: 24 pages, 12 figures, uses psfrag and hyperref; replaced with
published version, only minor corrections of typos and reference
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