A5040993175- Advanced Condensed Matter Physics
- Physics of Superconductivity and Magnetism
- Magnetic and transport properties of perovskites and related materials
- High-pressure geophysics and materials
- X-ray Spectroscopy and Fluorescence Analysis
- X-ray Diffraction in Crystallography
- Rare-earth and actinide compounds
- Crystallography and Radiation Phenomena
- Advanced X-ray Imaging Techniques
- Surface and Thin Film Phenomena
- Multiferroics and related materials
- Electron and X-Ray Spectroscopy Techniques
- Lipid Membrane Structure and Behavior
- Nuclear Physics and Applications
- Iron-based superconductors research
- Force Microscopy Techniques and Applications
- Superconducting Materials and Applications
- Theoretical and Computational Physics
- Magnetic properties of thin films
- Magnetic Properties of Alloys
- Molecular Junctions and Nanostructures
- Spectroscopy and Quantum Chemical Studies
- Nuclear materials and radiation effects
- Advanced Materials Characterization Techniques
- Electrochemical Analysis and Applications
Argonne National Laboratory
2014-2023
Washington State University
2018
Advanced Photon Source
2008
University of Pennsylvania
2005-2006
Brookhaven National Laboratory
2004-2005
Bar-Ilan University
2005
Deutsches Elektronen-Synchrotron DESY
1994-1995
Purdue University West Lafayette
1989-1990
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,...
The surface structure and thermodynamics of two ionic liquids, based on the 1-alkyl-3-methylimidazolium cations, were studied by X-ray reflectivity tensiometry. A molecular layer a density approximately 18% higher than that bulk is found to form at free these liquids. In common with layering in liquid metals freezing melts organic chain molecules, this effect induced lower dimensionality surface. concentrations oppositely charged ions within are determined chemical substitution anion....
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...
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...
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...
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...
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 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...
The detonation of carbon-rich high explosives yields solid carbon as a major constituent the product mixture, and depending on thermodynamic conditions behind shock front, variety allotropes morphologies may form evolve. We applied time-resolved small-angle X-ray scattering (TR-SAXS) to investigate dynamics clustering during PBX 9502, an explosive composed 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) 5 wt % fluoropolymer binder. Solid formation was probed from 0.1 2.0 μs front revealed rapid...
Vanadium sesquioxide, V2O3, is a prototypical metal-to-insulator system where, in temperature-dependent studies, the transition always coincides with corundum-to-monoclinic structural transition. As function of pressure, V2O3 follows expected behavior increased metallicity due to larger bandwidth for pressures up 12.5 GPa. Surprisingly, higher when structure becomes unstable, resistance starts increase. Around 32.5 GPa at 300 K, we observe novel pressure-induced between two metallic phases,...
Spin-orbit entangled magnetic dipoles, often referred to as pseudospins, provide a new avenue explore novel magnetism inconceivable in the weak spin-orbit coupling limit, but nature of their low-energy interactions remains be understood. We present comprehensive study static and pseudospin dynamics archetypal Mott insulator Sr2IrO4. find that order understand even basic magnetization measurements, formerly overlooked in-plane anisotropy is fundamental. In addition magnetometry, we use...
We have investigated the structural, electronic, and magnetic properties of pyrochlore iridates ${\mathrm{Eu}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ ${\mathrm{Pr}}_{2}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ using a combination resonant elastic x-ray scattering, powder diffraction, inelastic scattering (RIXS). The structural parameters been examined as function temperature applied pressure, with particular emphasis on regions phase diagram where electronic transitions reported. find no evidence...
Resonant inelastic X-ray scattering (RIXS) experiments require special sets of near-backscattering spherical diced analyzers and high-resolution monochromators for every distinct absorption-edge energy emission line. For the purpose aiding design planning efficient RIXS experiments, comprehensive lists suitable analyzer reflections silicon, germanium, α-quartz, sapphire lithium niobate crystals were compiled a multitude absorption edges lines. Analyzers made from niobate, or α-quartz offer...
We report a combined experimental and theoretical study of the unusual ferromagnetism in one-dimensional copper-iridium oxide Sr(3)CuIrO(6). Utilizing Ir L(3) edge resonant inelastic x-ray scattering, we reveal large gap magnetic excitation spectrum. find that it is caused by an exchange anisotropy generating mechanism, namely, strong ferromagnetic arising from antiferromagnetic superexchange, driven alternating weak spin-orbit coupling on 5d 3d Cu ions, respectively. From symmetry...
The spin-orbit Mott insulator Sr_{3}Ir_{2}O_{7} provides a fascinating playground to explore insulator-metal transition driven by intertwined charge, spin, and lattice degrees of freedom. Here, we report high-pressure electric resistance resonant inelastic x-ray scattering measurements on single-crystal up 63-65 GPa at 300 K. material becomes confined metal 59.5 GPa, showing metallicity in the ab plane but an insulating behavior along c axis. Such unusual phenomenon resembles strange phase...
Strong spin-orbit coupling lifts the degeneracy of t2g orbitals in 5d transition-metal systems, leaving a Kramers doublet and quartet with effective angular momentum Jeff = 1/2 3/2, respectively. These entangled states can host exotic quantum phases such as topological Mott state, unconventional superconductivity, spin liquid. The lacunar spinel GaTa4Se8 was theoretically predicted to form molecular 3/2 ground state. Experimental verification its existence is an important first step...
Recent measurements show that the free surfaces of liquid metals and alloys are always layered, regardless composition surface tension; a result supported by three decades simulations theory. theoretical work claims, however, at low enough temperatures all liquids should become unless preempted bulk freezing. Using x-ray reflectivity diffuse scattering we there is no observable surface-induced layering in water $T=298\mathrm{K},$ thus highlighting fundamental difference between dielectric...
We report a resonant inelastic x-ray scattering study of charge excitations in the quasi-one-dimensional Mott insulator ${\mathrm{SrCuO}}_{2}$. observe continuum low-energy excitations, onset which exhibits small dispersion $\ensuremath{\sim}0.4\text{ }\text{ }\mathrm{eV}$. Within this continuum, highly dispersive feature with large sinusoidal ($\ensuremath{\sim}1.1\text{ }\mathrm{eV}$) is observed. have also measured optical conductivity, and studied dynamic response extended Hubbard model...
We report a study of electronic excitations in manganites exhibiting range ground states, using resonant inelastic x-ray scattering (RIXS) at the Mn $K$ edge. Excitations with temperature dependent changes correlated magnetism were observed as high 10 eV. By calculating Wannier functions, and finite-$q$ response we associate this dependence intersite $d\mathrm{\text{\ensuremath{-}}}d$ excitations. The calculated dynamical structure factor is found to be similar RIXS spectra.