470 research outputs found
Observation of the Holstein shift in high superconductors with thermal modulation reflectometry
We use the experimental technique of thermal modulation reflectometry to
study the relatively small temperature dependence of the optical conductivity
of superconductors. Due to a large cancellation of systematic errors, this
technique is shown to a be very sensitive probe of small changes in
reflectivity. We analyze thermal modulation reflection spectra of single
crystals and epitaxially grown thin films of YBaCuO and
obtain the function in the normal state, as well as
the superconductivity induced changes in reflectivity. We present detailed
model calculations, based on the Eliashberg-Migdal extension of the BCS model,
which show good qualitative and quantitative agreement with the experimental
spectra. VSGD.93.12.thComment: 6 pages, figures on request. Revtex, version 2, Materials Science
Center Internal Report Number VSGD.93.12.t
ĐĐŸĐŽĐ”Đ»Đž ĐČĐ°Đ»ŃŃĐœĐŸĐłĐŸ ŃДгŃлОŃĐŸĐČĐ°ĐœĐžŃ Đž ĐžŃ ĐżŃĐžĐŒĐ”ĐœĐ”ĐœĐžĐ” ĐČ ŃĐŸŃŃĐžĐčŃĐșĐŸĐč ĐŽĐ”ĐčŃŃĐČĐžŃДлŃĐœĐŸŃŃĐž
ĐĐ°ĐœĐœĐ°Ń ŃŃĐ°ŃŃŃ ĐżĐŸŃĐČŃŃĐ”ĐœĐ° Đ°ĐșŃŃĐ°Đ»ŃĐœĐŸĐč ĐœĐ° ŃĐ”ĐłĐŸĐŽĐœŃŃĐœĐžĐč ĐŽĐ”ĐœŃ ŃĐ”ĐŒĐ” ŃĐ°Đ·ĐČĐžŃĐžŃ Đž ŃĐŸĐČĐ”ŃŃĐ”ĐœŃŃĐČĐŸĐČĐ°ĐœĐžŃ ĐČĐ°Đ»ŃŃĐœĐŸĐłĐŸ ŃДгŃлОŃĐŸĐČĐ°ĐœĐžŃ. Đ ĐœĐ°ŃŃĐŸŃŃДД ĐČŃĐ”ĐŒŃ Ń ŃŃĐ”ŃĐŸĐŒ ŃĐșĐŸĐœĐŸĐŒĐžŃĐ”ŃĐșĐŸĐč ŃĐžŃŃĐ°ŃОО ĐČ ŃŃŃĐ°ĐœĐ” ĐŽĐ°ĐœĐœĐ°Ń ŃĐ”ĐŒĐ° ĐČŃĐ·ŃĐČĐ°Đ”Ń ĐœĐ”ĐżĐŸĐŽĐŽĐ”Đ»ŃĐœŃĐč ĐžĐœŃĐ”ŃĐ”Ń, ŃĐ°Đș ĐșĐ°Đș ĐČĐ°Đ»ŃŃĐœĐŸĐ” ŃДгŃлОŃĐŸĐČĐ°ĐœĐžĐ” ŃĐČĐ»ŃĐ”ŃŃŃ ĐœĐ”ĐŸŃŃĐ”ĐŒĐ»Đ”ĐŒĐŸĐč ŃĐ°ŃŃŃŃ ĐŽĐ”ĐœĐ”Đ¶ĐœĐŸ-ĐșŃДЎОŃĐœĐŸĐč ĐżĐŸĐ»ĐžŃĐžĐșĐž ŃŃŃĐ°ĐœŃ, ŃĐČĐ»ŃĐ”ŃŃŃ ĐŒĐ”Ń
Đ°ĐœĐžĐ·ĐŒĐŸĐŒ, Ń ĐżĐŸĐŒĐŸŃŃŃ ĐșĐŸŃĐŸŃĐŸĐłĐŸ ŃŃабОлОзОŃŃĐ”ŃŃŃ ŃĐžĐœĐ°ĐœŃĐŸĐČĐ°Ń ŃĐžŃŃĐ°ŃĐžŃ, Đ° ŃĐ°ĐșжД ŃĐșŃДплŃĐ”ŃŃŃ ĐœĐ°ŃĐžĐŸĐœĐ°Đ»ŃĐœĐ°Ń ĐČĐ°Đ»ŃŃĐ°. ĐĄĐŸĐČĐ”ŃŃĐ”ĐœŃŃĐČĐŸĐČĐ°ĐœĐžĐ” ĐČĐ°Đ»ŃŃĐœĐŸĐłĐŸ ŃДгŃлОŃĐŸĐČĐ°ĐœĐžŃ ĐżŃОзĐČĐ°ĐœĐŸ ŃĐżĐŸŃĐŸĐ±ŃŃĐČĐŸĐČĐ°ŃŃ ĐżŃĐ”ĐŸĐŽĐŸĐ»Đ”ĐœĐžŃ ŃазлОŃĐœŃŃ
ĐșŃОзОŃĐœŃŃ
ŃĐžŃŃĐ°ŃĐžĐč ĐČ ŃŃŃĐ°ĐœĐ”, Đ° ŃĐ°ĐșжД ŃĐżĐŸŃĐŸĐ±ŃŃĐČŃĐ”Ń Đ±Đ»Đ°ĐłĐŸĐżŃĐžŃŃĐœĐŸĐŒŃ ŃĐ°Đ·ĐČĐžŃĐžŃ ŃĐșĐŸĐœĐŸĐŒĐžĐșĐž ĐČ ŃĐ”Đ»ĐŸĐŒ
Resonant x-ray diffraction study of the magnetoresistant perovskite Pr0.6Ca0.4MnO3
We report a x-ray resonant diffraction study of the perovskite
Pr0.6Ca0.4MnO3. At the Mn K-edge, this technique is sensitive to details of the
electronic structure of the Mn atoms. We discuss the resonant x-ray spectra
measured above and below the charge and orbital ordering phase transition
temperature (TCOO = 232 K), and present a detailed analysis of the energy and
polarization dependence of the resonant scattering. The analysis confirms that
the structural transition is a transition to an orbitally ordered phase in
which inequivalent Mn atoms are ordered in a CE-type pattern. The Mn atoms
differ mostly by their 3d orbital occupation. We find that the charge
disproportionation is incomplete, 3d^{3.5-\delta} and 3d^{3.5+\delta} with
\delta\ll0.5 . A revised CE-type model is considered in which there are two Mn
sublattices, each with partial e_{g} occupancy. One sublattice consists of Mn
atoms with the 3x^{2}-r^{2} or 3y^{2}-r^{2} orbitals partially occupied, the
other sublattice with the x^{2}-y^{2} orbital partially occupied.Comment: 15 pages, 15 figure
Usage Pattern Recognition in Student Activities
Proceedings of: 6th European Conference of Technology Enhanced Learning, EC-TEL 2011, Palermo, Italy, September 20-23, 2011.This paper presents an approach of collecting contextualized attention metadata combined from inside as well as outside a LMS and analyzing them to create feedback about the student activities for the teaching staff. Two types of analyses were run on the collected data: first, key actions were extracted to identify usage patterns and tendencies throughout the whole course and then usage statistics and patterns were identified for some key actions in more detail. Results of both analyses were visualized and presented to the teaching staff for evaluation.The research leading to these results has received funding
from the European Communityâs Seventh Framework Programme (FP7/2007-
2013) under grant agreement no 231396 (ROLE project). Work was also partially
funded by the Learn3 project (TIN2008-05163/TSI), the eMadrid project
(S2009/TIC-1650), and the AcciĂłn Integrada DE2009-0051
Charge order and low frequency spin dynamics in lanthanum cuprates revealed by Nuclear Magnetic Resonance
We report detailed 17O, 139La, and 63Cu Nuclear Magnetic Resonance (NMR) and
Nuclear Quadrupole Resonance (NQR) measurements in a stripe ordered
La1.875Ba0.125CuO4 single crystal and in oriented powder samples of
La1.8-xEu0.2SrxCuO4. We observe a partial wipeout of the 17O NMR intensity and
a simultaneous drop of the 17O electric field gradient (EFG) at low
temperatures where the spin stripe order sets in. In contrast, the 63Cu
intensity is completely wiped out at the same temperature. The drop of the 17O
quadrupole frequency is compatible with a charge stripe order. The 17O spin
lattice relaxation rate shows a peak similar to that of the 139La, which is of
magnetic origin. This peak is doping dependent and is maximal at x ~ 1/8.Comment: submitted to European Physical Journal Special Topic
Orbital ordering in the manganites: resonant x-ray scattering predictions at the manganese LII and LIII edges
It is proposed that the observation of orbital ordering in manganite materials should be possible at the L II and L III edges of manganese using x-ray resonant scattering. If performed, dipole selection rules would make the measurements much more direct than the disputed observations at the manganese K edge. They would yield specific information about the type and mechanism of the ordering not available at the K edge, as well as permitting the effects of orbital ordering and Jahn-Teller ordering to be detected and distinguished from one another. Predictions are presented based on atomic multiplet calculations, indicating distinctive dependence on energy, as well as on polarization and on the azimuthal angle around the scattering vector
Manganites at Quarter Filling: Role of Jahn-Teller Interactions
We have analyzed different correlation functions in a realistic spin-orbital
model for half-doped manganites. Using a finite-temperature diagonalization
technique the CE phase was found in the charge-ordered phase in the case of
small antiferromagnetic interactions between electrons. It is shown
that a key ingredient responsible for stabilization of the CE-type spin and
orbital-ordered state is the cooperative Jahn-Teller (JT) interaction between
next-nearest Mn neighbors mediated by the breathing mode distortion of
Mn octahedra and displacements of Mn ions. The topological phase
factor in the Mn-Mn hopping leading to gap formation in one-dimensional models
for the CE phase as well as the nearest neighbor JT coupling are not able to
produce the zigzag chains typical for the CE phase in our model.Comment: 16 pages with 16 figures, contains a more detailed parameter estimate
based on the structural data by Radaelli et al. (accepted for publication in
Phys. Rev. B
Glassy nature of stripe ordering in La(1.6-x)Nd(0.4)Sr(x)CuO(4)
We present the results of neutron-scattering studies on various aspects of
crystalline and magnetic structure in single crystals of
La(1.6-x)Nd(0.4)Sr(x)CuO(4) with x=0.12 and 0.15. In particular, we have
reexamined the degree of stripe order in an x=0.12 sample. Measurements of the
width for an elastic magnetic peak show that it saturates at a finite value
below 30 K, corresponding to a spin-spin correlation length of 200 A. A model
calculation indicates that the differing widths of magnetic and (previously
reported) charge-order peaks, together with the lack of commensurability, can
be consistently explained by disorder in the stripe spacing. Above 30 K, the
width of the nominally elastic signal begins to increase. Interpreting the
signal as critical scattering from slowly fluctuating spins, the temperature
dependence of the width is consistent with renormalized classical behavior of a
2-dimensional anisotropic Heisenberg antiferromagnet. Inelastic scattering
measurements show that incommensurate spin excitations survive at and above 50
K, where the elastic signal is neglible. We also report several results related
to the LTO-to-LTT transition.Comment: 13 pp, 2-col. REVTeX, 11 figures embedded with psfig; expanded
discussion of T-dep. of magnetic peak width; version to appear in Phys. Rev.
B (01Jun99
Search for direct production of charginos and neutralinos in events with three leptons and missing transverse momentum in âs = 7 TeV pp collisions with the ATLAS detector
A search for the direct production of charginos and neutralinos in final states with three electrons or muons and missing transverse momentum is presented. The analysis is based on 4.7 fbâ1 of protonâproton collision data delivered by the Large Hadron Collider and recorded with the ATLAS detector. Observations are consistent with Standard Model expectations in three signal regions that are either depleted or enriched in Z-boson decays. Upper limits at 95% confidence level are set in R-parity conserving phenomenological minimal supersymmetric models and in simplified models, significantly extending previous results
Jet size dependence of single jet suppression in lead-lead collisions at sqrt(s(NN)) = 2.76 TeV with the ATLAS detector at the LHC
Measurements of inclusive jet suppression in heavy ion collisions at the LHC
provide direct sensitivity to the physics of jet quenching. In a sample of
lead-lead collisions at sqrt(s) = 2.76 TeV corresponding to an integrated
luminosity of approximately 7 inverse microbarns, ATLAS has measured jets with
a calorimeter over the pseudorapidity interval |eta| < 2.1 and over the
transverse momentum range 38 < pT < 210 GeV. Jets were reconstructed using the
anti-kt algorithm with values for the distance parameter that determines the
nominal jet radius of R = 0.2, 0.3, 0.4 and 0.5. The centrality dependence of
the jet yield is characterized by the jet "central-to-peripheral ratio," Rcp.
Jet production is found to be suppressed by approximately a factor of two in
the 10% most central collisions relative to peripheral collisions. Rcp varies
smoothly with centrality as characterized by the number of participating
nucleons. The observed suppression is only weakly dependent on jet radius and
transverse momentum. These results provide the first direct measurement of
inclusive jet suppression in heavy ion collisions and complement previous
measurements of dijet transverse energy imbalance at the LHC.Comment: 15 pages plus author list (30 pages total), 8 figures, 2 tables,
submitted to Physics Letters B. All figures including auxiliary figures are
available at
http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/HION-2011-02
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