P. Abbamonte

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

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Publications (19)29.4 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.
    No preview · Article · Aug 2014 · Physical Review Letters
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    ABSTRACT: We have used x-ray diffraction to study the structure of strained, epitaxial ${\text{BiFeO}}_{3}$ (BFO) films, which exhibit ordered arrays of stripelike ferroelectric domains, in which the polarization vector P alternates by either 109${}^{$\circ${}}$ or 71${}^{$\circ${}}$. Diffraction maps exhibit an intricate satellite structure that arises from coherent, gratinglike diffraction from the domain structure. In the case of the 109${}^{$\circ${}}$ arrays, the domain structure was found to exert a strain modulation on the ${\text{DyScO}}_{3}$ substrate, with the same periodicity, indicating that domains in BFO can have an influence on the substrate structure. In the case of the 71${}^{$\circ${}}$ arrays, in which there is no contrast between neighboring domains and coherent scattering is not expected, weak scattering is nonetheless observed, which we interpret as evidence for previously unobserved, internal strains in these domain walls. To understand the x-ray data, we introduce a simple, single-scattering model that incorporates Gaussian disorder and fits the diffraction maps, providing domain periods and surface ``puckering'' angles that are in good agreement with atomic force microscopy and piezoresponse force microscopy measurements. Our study demonstrates a simple, computationally inexpensive technique for semiquantitatively interpreting coherent domain scattering in ferroelectric films, and suggests that tuning domain structures is a potential route to engineering the near-surface properties of perovskite oxides.
    No preview · Article · Jun 2014 · Physical Review B
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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).
    No preview · Article · May 2014 · Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

  • No preview · Article · Jun 2011
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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.
    Full-text · Article · Mar 2010 · Nuclear Fusion
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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.
    No preview · Article · May 2007 · Physical Review B
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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.
    Full-text · Article · Feb 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
    Preview · Article · Aug 2006 · Physical Review B
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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.
    Full-text · Article · Jun 2006 · Journal of Physics Condensed Matter
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    P. Abbamonte · A. Rusydi · S. Smadici · G. D. Gu · G. A. Sawatzky · D. L. Feng

    Preview · Article · Nov 2005
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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.
    Full-text · Article · Jan 2005

  • No preview · Article · Jan 2005
  • Peter M. Abbamonte · L. Venema · A. Rusydi · G. Logvenov · Ivan Bozovic · George A. Sawatzky
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    ABSTRACT: It has recently been shown that x-ray diffraction from the doped holes in cuprates can be enhanced by 3-4 orders of magnitude by exploiting resonance effects in the oxygen K shell. This new type of anomalous scattering is direct way of probing ground state inhomogeneity in the mobile carrier liquid of high temperature superconductors. Here we describe a model which quantifies the relationship between experimental count rates and the structure factor for doped holes in this technique. We describe first efforts to detect inhomogeneity in thin films of La2CuO4+delta and report some peculiar observations. We attempt to offer some explanation.
    No preview · Article · Nov 2002 · Proceedings of SPIE - The International Society for Optical Engineering
  • Kenneth D. Finkelstein · Peter M. Abbamonte · V. O. Kostroun
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    ABSTRACT: Following successful experience using photolithography and high aspect ratio reactive ion etching (RIE) to produce dynamically bent x-ray sagittal focusing crystals, we report on incorporating this optic in a novel high flux, narrow bandwidth, energy scanning monochromator for bend magnet synchrotron radiation. We describe the mono, several modes of operation, and our experience using it. Deep RIE has great utility for the manufacture, in silicon, of mechanical devices with feature as small as a few microns, however aberration free Bragg diffraction focusing requires uniformity in etch depth over large areas. To improve optical performance in terms of minimum focus spot size and maximum x-ray throughput, we are developing "second generation" focusing crystals based on a composite structure concept. We describe some of this new work and suggest areas of application.
    No preview · Article · Sep 2002 · Proceedings of SPIE - The International Society for Optical Engineering
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    ABSTRACT: We present results of low-temperature two-magnon resonance Raman excitation profile measurements for single layer Sr_2CuO_2Cl_2 and bilayer YBa_2Cu_3O_{6 + \delta} antiferromagnets over the excitation region from 1.65 to 3.05 eV. These data reveal composite structure of the two-magnon line shape and strong nonmonotic dependence of the scattering intensity on excitation energy. We analyze these data using the triple resonance theory of Chubukov and Frenkel (Phys. Rev. Lett., 74, 3057 (1995)) and deduce information about magnetic interaction and band parameters in these materials. Comment: REVTeX, 4 pages + 2 PostScript (compressed) figures
    Preview · Article · Jun 1996 · Physical review. B, Condensed matter
  • G. Blumberg · P. Abbamonte · M. V. Klein
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    ABSTRACT: We present results of low-temperature two-magnon resonance Raman excitation profile measurements for single layer Sr_2CuO_2Cl2 and bilayer YBa_2Cu_3O6 + δ antiferromagnets over the excitation region from 1.65 to 3.05 eV. These data reveal composite structure of the B_1g two-magnon line shape peaked at ~ 2.7J and ~ 4J and strong nonmonotonic dependence of the scattering intensity on excitation energy. Resonant magnetic scattering contributes also to A_1g and B_2g channels. We analyze these data using the triple resonance theory of Chubukov and Frenkel(A. Chubukov and D. Frenkel, Phys. Rev. Lett.74), 3057 (1995). and deduce information about magnetic interaction (J and J_⊥) and band parameters (NN hopping t and charge transfer gap 2Δ) in these antiferromagnets.(G. Blumberg et. al.), Preprint cond-mat/9511080. The ~ 3J spin superexchange excitation persists upon hole doping and is present in superconductors, proving the universality of the short wavelength magnetic excitations in the cuprate superconducting metals and the parent antiferromagnetic insulators.(G. Blumberg et. al.), Phys. Rev. B 49, 13 295 (1994).
    No preview · Article · Mar 1996
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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.
    Full-text · Article · Jul 1994
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    S Smadici · J C T Lee · P Abbamonte · A Rusydi · G Logvenov · I Bozovic
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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
    Full-text · Article ·