P. Abbamonte

University of Illinois, Urbana-Champaign, Urbana, Illinois, United States

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Publications (11)20.01 Total impact

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    ABSTRACT: We study the electronic screening mechanisms of the effective Coulomb on-site repulsion in hole-doped Sr_{14}Cu_{24}O_{41} compared to undoped La_{6}Ca_{8}Cu_{24}O_{41} using polarization dependent high-resolution resonant inelastic x-ray scattering at Cu M edges. By measuring the energy of the effective Coulomb on-site repulsion and the spin excitations, we estimate superexchange and hopping matrix element energies along rungs and legs, respectively. Interestingly, hole doping locally screens the Coulomb on-site repulsion reducing it by as much as 25%. We suggest that the increased ratio of the electronic kinetic to the electronic correlation energy contributes to the local superexchange mediated pairing between holes.
    Physical Review Letters 08/2014; 113(6):067001. · 7.73 Impact Factor
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    ABSTRACT: The optical design of the Intermediate Energy X-ray (IEX) beamline at the APS has been optimized to study emergent phenomena via angle-resolved photoemission spectroscopy (ARPES) and resonant soft X-ray scattering (RSXS). Driven by the scientific requirements of these two techniques the beamline consists of two separate branchlines sharing the same source, heat absorbing optics and monochromator, but each having its own refocusing optics. The ARPES branch is optimized for a very high “resolving power” and a small spot at the sample; whereas, the RSXS branch is designed for high flux and a low beam divergence at the sample. The very high “resolving power” in the ARPES branch is achieved by using a monochromator which consists of a plane mirror and a variable line spacing grating that focuses the beam at all photon energies. A flux higher than 10101010 photons/s at a “resolving power” better than 5×104 will be available at the sample position of the ARPES beamline on a spot size (FWHM) smaller than 21×4μm2 (hor.×ver.) for photon energies between 250 and 1660 eV. A second grating will increase the flux by more than a factor of 10 at a “resolving power” of 104. The flux expected at the RSXS branch for energies between 250 eV and 1900 eV is higher than 4×1012 photons/s at “resolving power” around 2.5×103. The expected spot in this branch is sub-millimeter and the beam divergence is less than 0.3 mrad (FWHM).
    01/2014; 746:98–105.
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    ABSTRACT: We explore a method for constructing two-dimensional area-preserving, integrable maps associated with Hamiltonian systems, with a given set of fixed points and given invariant curves. The method is used to find an integrable Poincaré map for the field lines in a large aspect ratio tokamak with a poloidal single-null divertor. The divertor field is a superposition of a magnetohydrodynamic equilibrium with an arbitrarily chosen safety factor profile, with a wire carrying an electric current to create an X-point. This integrable map is perturbed by an impulsive perturbation that describes non-axisymmetric magnetic resonances at the plasma edge. The non-integrable perturbed map is applied to study the structure of the open field lines in the scrape-off layer, reproducing the main transport features obtained by integrating numerically the magnetic field line equations, such as the connection lengths and magnetic footprints on the divertor plate.
    Nuclear Fusion 01/2010; 50. · 2.73 Impact Factor
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    ABSTRACT: Soft x-ray resonant scattering has been used to examine the charge and magnetic interactions in the cycloidal antiferromagnetic compound DyFe4Al8 . By tuning to the Dy M4 and M5 absorption edges and the Fe L2 and L3 absorption edges, we can directly observe the behavior of the Dy 4f and Fe 3d electron shells. Magnetic satellites surrounding the (110) Bragg peak were observed below 65K . The diffraction peaks display complex spectra at the Dy M5 edge, indicative of a split 4f electron band. This is in contrast to the simple resonance observed at the Fe L3 absorption edge, which probes the Fe 3d electron shell. Temperature-dependent measurements detail the ordering of the magnetic moments on both the iron and the dysprosium antiferromagnetic cycloids. The ratio between the superlattice peak intensities of the Dy M4 and M5 absorption edges remained constant throughout the temperature range, in contrast to a previous study conducted at the Dy L2,3 edges. Our results demonstrate the ability of soft x-ray diffraction to separate the individual magnetic components in complicated multielement magnetic structures.
    Physical Review B 05/2007; 75(17). · 3.66 Impact Factor
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    ABSTRACT: Soft x-ray resonant scattering has been used to examine the charge and magnetic interactions in the cycloidal antiferromagnetic compound \dyfeal. By tuning to the Dy $M_4$ and $M_5$ absorption edges and the Fe L(2) and L(3) absorption edges we can directly observe the behavior of the Dy 4f and Fe 3d electron shells. Magnetic satellites surrounding the (110) Bragg peak were observed below 60 K. The diffraction peaks display a complex spectra at the Dy M(5) edge, indicative of a split 4f electron band. This is in contrast to a simple resonance observed at the Fe L(3) absorption edge, which probes the Fe 3d electron shell. Temperature dependant measurements detail the ordering of the magnetic moments on both the iron and the dysprosium antiferromagnetic cycloids. The ratio between the intensities of the Dy M(4) and M(5) remained constant throughout the temperature range, in contrast to a previous study conducted at the Dy L(2,3) edges. Our results demonstrate the ability of soft x-ray diffraction to separate the individual magnetic components in complicated multi-element magnetic structures.
    02/2007;
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    P. Abbamonte
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    ABSTRACT: A method is described for using resonant x-ray scattering to separately quantify the charge (valence) modulation and the strain wave associated with a charge density wave. The essence of the method is a separation of the atomic form factor into a "raw" amplitude, fR(w), and a valence-dependent amplitude, fD(w), which in many cases may be determined independently from absorption measurements. The advantage of this separation is that the strain wave follows the quantity |fR(w) + fD(w)|^2 whereas the charge modulation follows only |fD(w)|^2. This allows the two distinct modulations to be quantified separately. A scheme for characterizing a given CDW as Peierls-like or Wigner-like naturally follows. The method is illustrated for an idealized model of a one-dimensional chain. Comment: 6 pages, 4 figures
    Physical Review B 08/2006; · 3.66 Impact Factor
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    ABSTRACT: Resonant soft x-ray diffraction has been used to probe the temperature dependent orbital and magnetic structure of LaSr2Mn2O7. Previous crystallographic studies have shown that this material has almost no MnO6 oxygen displacements due to Jahn–Teller distortions at low temperatures. Within the low-temperature A-type antiferromagnetic phase, we found strong intensity at the () orbital and (0, 0, 1) magnetic reflections. This shows that even in the near absence of Jahn–Teller distortions, this compound is strongly orbitally ordered. A fit to the Mn L-edge resonance spectra demonstrates the presence of orbital ordering of the Mn3+ ions with virtually no Jahn–Teller crystal field in addition to possible Mn3+ and Mn2+-like valence fluctuations.
    Journal of Physics Condensed Matter 06/2006; 18(24):L323. · 2.22 Impact Factor
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    ABSTRACT: Resonant soft x-ray diffraction has been used to probe the temperature dependent orbital and magnetic structure of $\mathrm{LaSr_{2}Mn_{2}O_7}$. Previous crystallographic studies have shown that this material has almost no MnO$_{6}$ oxygen displacement due to Jahn-Teller distortions at low temperatures. Within the low-temperature A-type antiferromagnetic phase, we found strong intensity at the $({1/4},{1/4},0)$ orbital and $LaSr_{2}Mn_{2}O_7$ magnetic reflections. This shows that even in the near absence of Jahn-Teller distortion, this compound is strongly orbitally ordered. A fit to the Mn $L$-edge resonance spectra demonstrates the presence of orbital ordering of the Mn$^{3+}$ ions with virtually no Jahn-Teller crystal field in addition to possible Mn$^{3+}$ and Mn$^{2+}$~like valence fluctuations.
    01/2005;
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    Peter M Abbamonte, P J Morrison
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    ABSTRACT: Various methods of constructing two-dimensional, area-preserving maps of general Hamiltonian systems are explored. Emphasis is on constructing maps with a given set of fixed points, a given invariant curve, or a given topology, and also on guaranteeing integrability. One method is used to find an integrable Poincare map for the field lines in a tokamak with a single null-divert or where the q-profiles can be arbitrarily chosen.
    IFSR. 07/1994; 638.
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    ABSTRACT: X-ray absorption in Sr2CuO 4−δ −La2CuO4 (SCO-LCO) superlattices shows a variable occupation with doping of a hole state different from holes doped for x x optimal in bulk La2−xSrxCuO4 and suggests that this hole state is on apical oxygen atoms and polarized in the a − b plane. Considering the surface reflectivity gives a good qualitative description of the line shapes of resonant soft X-ray scattering. The interference between superlattice and surface reflections was used to distinguish between scatterers in the SCO and the LCO layers, with the two hole states maximized in different layers of the superlattice.
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    ABSTRACT: We explore a method for constructing two-dimensional area-preserving, integrable maps associ- ated with Hamiltonian systems, with a given set of