1,184 research outputs found
Evolution of Mid-gap States and Residual 3-Dimensionality in LaSrCuO
We have carried out extensive first principles doping-dependent computations
of angle-resolved photoemission (ARPES) intensities in LaSrCuO
(LSCO) over a wide range of binding energies. Intercell hopping and the
associated 3-dimensionality, which is usually neglected in discussing cuprate
physics, is shown to play a key role in shaping the ARPES spectra. Despite the
obvious importance of strong coupling effects (e.g. the presence of a lower
Hubbard band coexisting with mid-gap states in the doped insulator), we show
that a number of salient features of the experimental ARPES spectra are
captured to a surprisingly large extent when effects of -dispersion are
properly included in the analysis.Comment: 5 pages, 4 figure
Matrix Element and Strong Electron Correlation Effects in ARPES from Cuprates
We discuss selected results from our recent work concerning the ARPES
(angle-resolved photoemission) spectra from the cuprates. Our focus is on
developing an understanding of the effects of the ARPES matrix element and
those of strong electron correlations in analyzing photointensities. With
simulations on BiSrCaCuO (Bi2212), we show that the
ARPES matrix element possesses remarkable selectivity properties, such that by
tuning the photon energy and polarization, emission from the bonding or the
antibonding states can be enhanced. Moreover, at low photon energies (below 25
eV), the Fermi surface (FS) emission is dominated by transitions from just the
O-atoms in the CuO planes. In connection with strong correlation effects,
we consider the evolution with doping of the FS of
NdCeCuO (NCCO) in terms of the -- Hubbard
model Hamiltonian. We thus delineate how the FS evolves on electron doping from
the insulating state in NCCO. The Mott pseudogap is found to collapse around
optimal doping suggesting the existence of an associated quantum critical
point.Comment: 5 pages, 4 figures, accepted to be published in Journal of Physics
and Chemistry of Solid
Beam Dynamics Studies for the HIE-ISOLDE Linac at CERN
The upgrade of the normal conducting (NC) Radioactive Ion Beam EXperiment
(REX)-ISOLDE heavy ion accelerator at CERN, under the High Intensity and Energy
(HIE)-ISOLDE framework, proposes the use of superconducting (SC) quarter-wave
resonators (QWRs) to increase the energy capability of the facility from 3
MeV/u to beyond 10 MeV/u. A beam dynamics study of a lattice design comprising
SC QWRs and SC solenoids has confirmed the design's ability to accelerate ions,
with a mass-to-charge ratio in the range 2.5 < A/q < 4.5, to the target energy
with a minimal emittance increase. We report on the development of this study
to include the implementation of realistic fields within the QWRs and
solenoids. A preliminary error study is presented in order to constrain
tolerances on the manufacturing and alignment of the linac.Comment: 3 pages, 8 figures, 1 table, submitted to the Particle Accelerator
Conference (PAC) 2009 in Vancouver. Page formatting changed to US letter siz
Mismatch between the PSB and CPS due to the present vertical recombination scheme
The production of the nominal LHC beam will deamand optimum emittance preservation between individual machines in the injection chain. The edge effects at the entry and exit of the bending magnets used for the vertical recombination of the four PS booster rings to the level of the CPS results in a small uncompensated, and for each ring different, mismatch. We present recent measurements of the mismatch done in the PSB measurement line
Physics opportunities with future proton accelerators at CERN
We analyze the physics opportunities that would be made possible by upgrades
of CERN's proton accelerator complex. These include the new physics possible
with luminosity or energy upgrades of the LHC, options for a possible future
neutrino complex at CERN, and opportunities in other physics including rare
kaon decays, other fixed-target experiments, nuclear physics and antiproton
physics, among other possibilities. We stress the importance of inputs from
initial LHC running and planned neutrino experiments, and summarize the
principal detector R&D issues.Comment: 39 page, word document, full resolution version available from
http://cern.ch/pofpa/POFPA-arXive.pd
"Intelligent" Automatic Beam Steering and Shaping
The strategy for Automated Beam Steering and Shaping (ABS) in the PS complex is to use theoretical response matrices calculated from an optics database. The main reason for this is that it enforces a certain understanding of the machine optics. A drawback is that the validation of such a matrix can be a lengthy process. However, every time a correction is made using an ABS program, a partial measurement of the response matrix is effectively performed. Since the ABS programs are very frequently used, the full matrices could thus be measured on an almost daily basis, provided this information is retained. The information can be used in two ways. Either the program passively logs the data to be analysed offÂline, or the information is directly fed back to the matrix, which makes the program 'learn' as it executes. The data logging provides a powerful machine debugging tool, since deviations between the measured and theoretical matrices can be traced back to incorrect optical parameters. The 'learning' mode ensures that the correction will always converge. Implementation details and simulation results are discussed
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