A5013413116- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- High-pressure geophysics and materials
- Rare-earth and actinide compounds
- X-ray Spectroscopy and Fluorescence Analysis
- X-ray Diffraction in Crystallography
- Multiferroics and related materials
- Electronic and Structural Properties of Oxides
- Crystallography and Radiation Phenomena
- Electron and X-Ray Spectroscopy Techniques
- Iron-based superconductors research
- Graphene research and applications
- Advancements in Photolithography Techniques
- Advanced X-ray Imaging Techniques
- Magnetic properties of thin films
- Theoretical and Computational Physics
- Organic and Molecular Conductors Research
- Magnetic Properties of Alloys
- Carbon Nanotubes in Composites
- Nuclear materials and radiation effects
- Metal-Catalyzed Oxygenation Mechanisms
- Crystal Structures and Properties
- Topological Materials and Phenomena
- Quantum and electron transport phenomena
Advanced Photon Source
2008-2024
Advanced Photonix (United States)
2024
Argonne National Laboratory
2014-2023
Lehigh University
2007
National Institute of Standards and Technology
2003-2006
University of Michigan
2006
University of California, Santa Barbara
2005
Pacific Northwest National Laboratory
2005
Brookhaven National Laboratory
2001-2004
Brookhaven College
2001-2002
We used resonant inelastic x-ray scattering to reveal the nature of magnetic interactions in Sr2IrO4, a 5d transition-metal oxide with spin-orbit entangled ground state and Jeff=1/2 momemts, referred as 'isospins'. The magnon dispersion Sr2IrO4 is well described by an antiferromagnetic Heisenberg model isospin one-half moments on square lattice, which renders low-energy effective physics much akin that superconducting cuprates. This further supported observation exciton modes whose strongly...
The electronic structure of the honeycomb lattice iridates ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ and ${\mathrm{Li}}_{2}{\mathrm{IrO}}_{3}$ has been investigated using resonant inelastic x-ray scattering (RIXS). Crystal-field-split $d\mathrm{\text{\ensuremath{-}}}d$ excitations are resolved in high-resolution RIXS spectra. In particular, splitting due to noncubic crystal fields, derived from ${j}_{\mathrm{eff}}=3/2$ states, is much smaller than typical spin-orbit energy scale iridates,...
A neutron scattering study of the Mott-Hubbard insulator LaTiO3 ( T(N) = 132 K) reveals a spin wave spectrum that is well described by nearest-neighbor superexchange constant J 15.5 meV and small Dzyaloshinskii-Moriya interaction D 1.1 meV). The nearly isotropic surprising in view absence static Jahn-Teller distortion could quench orbital angular momentum, it may indicate strong fluctuations. resonant x-ray has uncovered no evidence order LaTiO3.
Using resonant inelastic x-ray scattering, we observe in the bilayer iridate ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$, a spin-orbit coupling driven magnetic insulator with small charge gap, magnon gap of $\ensuremath{\approx}92\text{ }\text{ }\mathrm{meV}$ for both acoustic and optical branches. This exceptionally large exceeds total bandwidth $\ensuremath{\approx}70\text{ implies marked departure from Heisenberg model, stark contrast to case single-layer...
Electrons in graphene behave like Dirac fermions, permitting phenomena from high energy physics to be studied a solid state setting. A key question is whether or not these Fermions are critically influenced by Coulomb correlations. We performed inelastic x-ray scattering experiments on crystals of graphite, and applied reconstruction algorithms image the dynamical screening charge freestanding, sheet. found that polarizability fermions amplified excitonic effects, improving interactions...
We report a Fe K$\ensuremath{\beta}$ x-ray emission spectroscopy study of local magnetic moments in various iron-based superconductors their paramagnetic phases. Local are found all samples studied: PrFeAsO, $\mathrm{Ba}{(\mathrm{Fe},\mathrm{Co})}_{2}{\mathrm{As}}_{2}$, LiFeAs, Fe${}_{1+x}$(Te,Se), and ${\mathrm{A}}_{2}{\mathrm{Fe}}_{4}{\mathrm{Se}}_{5}$ (where $\text{A}=\text{K}$, Rb, Cs). The moment size is independent temperature or carrier concentration but varies significantly across...
The formation of high-valent states is a key factor in making highly active transition-metal-based catalysts the oxygen evolution reaction (OER). These high oxidation will be strongly influenced by local geometric and electronic structures metal ion, which are difficult to study due spectroscopically complex backgrounds, short lifetimes, limited concentrations. Here, we use wide range complementary X-ray spectroscopies coupled DFT calculations Co(III)4O4 cubanes their first oxidized...
We report resonant x-ray scattering studies of charge and orbital order in ${\mathrm{Pr}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ with $x\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}0.4$ 0.5. Below the ordering temperature, ${T}_{O}\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}245\mathrm{K}$, intensities follow same temperature dependence, including an increase at antiferromagnetic ${T}_{N}$. High resolution measurements reveal, however, that long range is never...
A complete, continuous transition from discrete macroions to blackberry structures, and then back macroions, is reported for the first time in system of {Mo132}/water/acetone, with {Mo132} (full formula (NH4)42[Mo132O372(CH3COO)30(H2O)72].ca.300H2O.ca.10CH3COONH4) as C60-like anionic polyoxomolybdate molecular clusters. Laser light scattering studies reveal presence self-assembled structures water/acetone mixed solvents containing 3 vol % 70 acetone, average hydrodynamic radius (Rh)...
Utilizing resonant inelastic x-ray scattering, we report a previously unobserved mode in the excitation spectrum of ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CuO}}_{4}$ and ${\mathrm{Nd}}_{2}{\mathrm{CuO}}_{4}$ at 500 meV. The is peaked around ($\ensuremath{\pi}$, 0) point reciprocal space observed to soften, broaden, away from this point. Samples with $x=0$, 0.01, 0.05, 0.17 were studied. new found be rapidly suppressed increasing Sr content absent $x=0.17$, where it...
The electronic structure of ${\mathrm{Sr}}_{3}{\mathrm{CuIrO}}_{6}$, a model system for the $5d$ Ir ion in an octahedral environment, is studied through combination resonant inelastic x-ray scattering and theoretical calculations. Resonant spectra at ${L}_{3}$ edge reveal ${t}_{2g}$ manifold that split into three levels, contrast to expectations strong spin-orbit-coupling limit. Effective Hamiltonian ab inito quantum chemistry calculations find strikingly large noncubic crystal field...
The low energy excitations in ${\mathrm{Na}}_{2}{\mathrm{IrO}}_{3}$ have been investigated using resonant inelastic x-ray scattering (RIXS). A magnetic excitation branch can be resolved, whose dispersion reaches a maximum of about 35 meV at the $\ensuremath{\Gamma}$ point. momentum dependence is much larger along $\ensuremath{\Gamma}\ensuremath{-}X$ direction compared to that $\ensuremath{\Gamma}\ensuremath{-}Y$ direction. observed relation consistent with recent theoretical prediction based...
We have used a combination of resonant magnetic x-ray scattering (RMXS) and absorption spectroscopy (XAS) to investigate the properties doped spin-orbital Mott insulator Sr2Ir(1-x)Rh(x)O4 (0.07 < x 0.70). show that represents unique model system for study dilute magnetism in presence strong spin-orbit coupling, provide evidence doping-induced change structure suppression order at x_c ~ 0.17. demonstrate Rh-doping introduces Rh3+/Ir5+ ions which effectively hole-dope this material. propose...
In the search for topological phases in correlated electron systems, materials with $5d$ transition-metal ions, particular iridium-based pyrochlores ${A}_{2}$Ir${}_{2}$O${}_{7}$, provide fertile grounds. Several states have been predicted but actual realization of such is believed to critically depend on strength local potentials arising from distortions IrO${}_{6}$ cages. We test this hypothesis by measuring resonant inelastic x-ray scattering electronic level splittings $A=\text{Y}$, Eu...
The rich physics manifested by 5d oxides falls outside the Mott-Hubbard paradigm used to successfully explain electronic and magnetic properties of 3d oxides. Much consideration has been given extent which strong spin-orbit coupling (SOC), in limit increased bandwidth reduced electron correlation, drives formation novel states, as through existence metal-insulator transitions (MITs). SOC is believed play a dominant role 5d5 systems such iridates (Ir4+), undergoing MITs may or not be...
We report resonant inelastic x-ray scattering (RIXS) measurements on ordered double-perovskite samples containing ${\mathrm{Re}}^{5+}$ and ${\mathrm{Ir}}^{5+}$ with $5{d}^{2}$ $5{d}^{4}$ electronic configurations, respectively. In particular, the observed RIXS spectra of ${\mathrm{Ba}}_{2}{\mathrm{YReO}}_{6}$ ${\mathrm{Sr}}_{2}M{\mathrm{IrO}}_{6}$ ($M$ = Y, Gd) show sharp intra-${t}_{2g}$ transitions, which can be quantitatively understood using a minimal ``atomic'' Hamiltonian incorporating...
The 5d^{1} ordered double perovskites present an exotic playground for studying novel multipolar physics due to large spin-orbit coupling. We Re L_{3} edge resonant inelastic x-ray scattering (RIXS) results that reveal the presence of dynamic Jahn-Teller effect in A_{2}MgReO_{6} (A=Ca, Sr, Ba) family perovskites. excitations these materials show a strongly asymmetric line shape and exhibit substantial temperature dependence, indicating they are dressed with lattice vibrations. Our...
We report a resonant inelastic x-ray scattering study of the dispersion relations charge-transfer excitations in insulating La(2)CuO(4).. These data reveal two peaks, both which show two-dimensional characteristics. The lowest energy excitation has gap approximately 2.2 eV at zone enter, and 1 eV. spectral weight this mode becomes dramatically smaller around (pi, pi). second peak shows ( 0.5 eV) with zone-center 3.9 argue that these are highly dispersive exciton modes damped by presence...
We present the results of a systematic x-ray scattering study charge and orbital ordering in manganite series Pr$_{1-x}$Ca$_x$MnO$_3$ with $x$=0.25, 0.4 0.5. The temperature dependence at wavevectors, lattice constants, was characterized throughout ordered phase each sample. It found that order wavevectors are commensurate lattice, striking contrast to earlier electron diffraction studies samples $x$=0.5. High momentum-transfer resolution x=0.4 0.5 further revealed while long-range is...
We report a resonant x-ray-diffraction study of the magnetoresistant perovskite ${\mathrm{Pr}}_{0.6}{\mathrm{Ca}}_{0.4}{\mathrm{MnO}}_{3}.$ discuss spectra measured above and below semiconductor-insulator transition temperature with aid detailed formal analysis energy polarization dependences structure factors ab initio calculations spectra. In low-temperature insulating phase, we find that inequivalent Mn atoms order in CE-type pattern crystallographic...
We report x-ray resonant magnetic scattering and inelastic studies of epitaxially strained ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$ thin films. The films were grown on ${\mathrm{SrTiO}}_{3}$ $({\mathrm{LaAlO}}_{3}{)}_{0.3}({\mathrm{Sr}}_{2}{\mathrm{AlTaO}}_{6}{)}_{0.7}$ substrates, under slight tensile compressive strains, respectively. Although the develop a structure reminiscent bulk ${\mathrm{Sr}}_{2}{\mathrm{IrO}}_{4}$, correlations are extremely anisotropic, with in-plane correlation...
Axial Cu-S(Met) bonds in electron transfer (ET) active sites are generally found to lower their reduction potentials. An axial S(Met) bond is also present cytochrome c (cyt c) and thought increase the potential. The highly covalent nature of porphyrin environment heme proteins precludes using many spectroscopic approaches directly study Fe site experimentally quantify this bond. Alternatively, L-edge X-ray absorption spectroscopy (XAS) enables one focus on 3d-orbitals a has previously been...