32 research outputs found
Local Electronic and Magnetic Structure of Ni below and above TC: A Spin-Resolved Circularly Polarized Resonant Photoemission Study
We report the measurement of the local Ni 3d spin polarization, not only below but also above the
Curie temperature (TC), using the newly developed spin-resolved circularly polarized 2p (L3) resonant
photoemission technique. The experiment identifies the presence of 3d8 singlets at high energies and
3d8 triplets at low energies extending all the way to the Fermi energy, both below and above TC,
showing that it is the orbital degeneracy of the 3d band and the Hund's rule splitting which is of utmost
importance to understand Ni and other 3d ferromagnets
Spin-Resolved Photoemission on Anti-Ferromagnets: Direct Observation of Zhang-Rice Singlets in CuO
We demonstrate that it is possible to obtain spin-resolved valence band spectra with a very high
degree of spin polarization from antiferromagnetic transition metal materials if the excitation light is
circularly polarized and has an energy close to the cation 2p3/2 (L3) white line. We are able to unravel
the different spin states in the single-particle excitation spectrum of CuO and show that the top of the
valence band is of pure singlet character, which provides strong support for the existence and stability
of Zhang-Rice singlets in high-Tc superconductors
Emissioin of Intermediate Mass Fragments During Fission
This research was sponsored by the National Science Foundation Grant NSF PHY-931478
One- and many-body effects on mirages in quantum corrals
Recent interesting experiments used scanning tunneling microscopy to study
systems involving Kondo impurities in quantum corrals assembled on Cu or noble
metal surfaces. The solution of the two-dimensional one-particle Schrodinger
equation in a hard wall corral without impurity is useful to predict the
conditions under which the Kondo effect can be projected to a remote location
(the quantum mirage). To model a soft circular corral, we solve this equation
under the potential W*delta(r-r0), where r is the distance to the center of the
corral and r0 its radius. We expand the Green's function of electron surface
states Gs0 for r<r0 as a discrete sum of contributions from single poles at
energies epsilon_i-I*delta_i. The imaginary part delta_i is the half-width of
the resonance produced by the soft confining potential, and turns out to be a
simple increasing function of epsilon_i. In presence of an impurity, we solve
the Anderson model at arbitrary temperatures using the resulting expression for
Gs0 and perturbation theory up to second order in the Coulomb repulsion U. We
calculate the resulting change in the differential conductance Delta dI/dV as a
function of voltage and space, in circular and elliptical corrals, for
different conditions, including those corresponding to recent experiments. The
main features are reproduced. The role of the direct hybridization between
impurity and bulk, the confinement potential, the size of the corral and
temperature on the intensity of the mirage are analyzed. We also calculate
spin-spin correlation functions.Comment: 13 pages, 12 figures, accepted for publication in Phys. Rev. B.
Calculations of spin correlations within an additional approximation adde
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THE REVITALIZED NSLS VUV RING.
A status report on the revitalization of the NSLS VUV ring will be presented, concentrating on three areas: (1) the four infrared ports (U2A/B, U4IR, U10A/B, and U12IR), (2) conversion of out-of-date toroidal grating monochromators to spherical grating type (U4A, U7A, and U12A), and (3) new insertion device beamlines (U5UA and U13UB). All of these beamlines were designed (new ones) or upgraded (old ones) to serve a specific scientific need represented by the PRTs (both NSLS and non-NSLS based) involved. Therefore, an overview of the scientific programs served by these new beamlines will be given, as well as a summary of the beamline optical designs and operating performance
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The revitalized NSLS VUV ring
A status report on the revitalization of the NSLS VUV ring will be presented, concentrating on three areas: (1) the four infrared ports (U2A/B, U4IR, U10A/B, and U12IR), (2) conversion of out-of-date toroidal grating monochromators to spherical grating type (U4A, U7A, and U12A), and (3) new insertion device beamlines (U5UA and U13UB). All of these beamlines were designed (new ones) or upgraded (old ones) to serve a specific scientific need represented by the PRTs (both NSLS and non-NSLS based) involved. Therefore, an overview of the scientific programs served by these new beamlines will be given, as well as a summary of the beamline optical designs and operating performance
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Interaction of InGa liquid alloy coolant with gold coated optical materials
A significant reaction is reported between gold surfaces and an indium-gallium eutectic liquid alloy often used to transfer heat away from optical elements in high power synchrotron radiation beamlines. This reaction proceeds at the slightly elevated temperatures (70{degrees}C) typical of conservative bakeouts used to achieve ultrahigh vacuum in the chambers which house these optical elements (mirrors, gratings, and crystals) without damaging their highly precise figure and finish. The nature and extent of this reaction is discussed, based mostly on the experience gained recently during the vacuum commissioning of two mirror chambers for a VUV wiggler-based synchrotron radiation beamline. 2 refs., 5 figs
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Mirror and grating surface figure requirements for grazing incidence synchrotron radiation beamlines: Power loading effects
At present, grazing incidence mirrors are used almost exclusively as the first optical element in VUV and soft x-ray synchrotron radiation beamlines. The performance of these mirrors is determined by thermal and mechanical stress-induced figure errors as well as by figure errors remaining from the grinding and polishing process. With the advent of VUV and soft x-ray undulators and wigglers has come a new set of thermal stress problems related to both the magnitude and the spatial distribution of power from these devices. In many cases the power load on the entrance slits and gratings in these beamlines is no longer negligible. The dependence of thermally-induced front-end mirror figure errors on various storage ring and insertion device parameters (especially those at the National Synchrotron Light Source) and the effects of these figure errors on two classes of soft x-ray beamlines are presented
Line shape of the Ag N23W Auger spectrum measured by Auger-photoelectron coincidence spectroscopy
We present Ag N3VV and N2VV Auger spectra obtained in coincidence with 4p3/2 and 4p1/2 core photoelectrons, respectively. We have also obtained the 4p3/2 and 4p1/2 core level spectra in coincidence with N3VV and N2VV Auger electrons. As the on-site Coulomb correlation energy of Ag, U, is comparable to the 4d band width, W, the coincidence Auger spectra exhibit aspects of both atomic-like and band-like components. We find a surprisingly large ~ 30% of the spectral weight of 2-hole decays is in the band-like region. Furthermore, the Auger spectra have large low energy tails that are atrributed to nonradiative decays involving more than two electrons. In the coincidence core level spectra, the large (> 5 eV) lifetime broadening is eliminated, leaving a width of 2.5 eV associated with the Auger lifetime. This sharp peak in the coincidence photoemission spectrum resides on a broader feature owing to the properties of the Auger transitions
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National Synchrotron Light Source annual report 1991
This report contains abstracts from research conducted at the national synchrotron light source. (LSP