A5037715094- Advanced Condensed Matter Physics
- Magnetic and transport properties of perovskites and related materials
- Physics of Superconductivity and Magnetism
- Electronic and Structural Properties of Oxides
- Magnetic properties of thin films
- Electron and X-Ray Spectroscopy Techniques
- Multiferroics and related materials
- Advanced Chemical Physics Studies
- Surface and Thin Film Phenomena
- Rare-earth and actinide compounds
- Phase-change materials and chalcogenides
- Inorganic Fluorides and Related Compounds
- High-pressure geophysics and materials
- Iron-based superconductors research
- Quantum and electron transport phenomena
- nanoparticles nucleation surface interactions
- Advanced Materials Characterization Techniques
- Inorganic Chemistry and Materials
- Catalytic Processes in Materials Science
- Advanced X-ray and CT Imaging
- Magnetic Properties and Applications
- Topological Materials and Phenomena
- Optical Network Technologies
- Crystallography and Radiation Phenomena
- ZnO doping and properties
University of Louisville
2013-2023
University of Illinois Urbana-Champaign
2007-2014
Brookhaven National Laboratory
2005-2007
Columbia University
2001-2005
We use resonant soft-x-ray scattering (RSXS) to study the electronic reconstruction at interface between Mott insulator LaMnO3 and band SrMnO3. Superlattices of these two insulators were shown previously have both ferromagnetism metallic tendencies [Koida, Phys. Rev. B 66, 144418 (2002)10.1103/PhysRevB.66.144418]. By studying a judiciously chosen superlattice reflection, we show that density states exhibits pronounced peak Fermi level, similar predicted in related titanate superlattices by...
A mutual ferromagnetic and ferroelectric coupling (multiferroic behavior) in Cu-doped ZnO is demonstrated via deterministic control of Cu doping defect engineering. The coexistence multivalence ions oxygen vacancies important to multiferroic behaviors ZnO:Cu. samples show clear domain patterns. These structures may be written reversibly electric magnetic bias. Detailed facts importance specialist readers are published as "Supporting Information". Such documents peer-reviewed, but not...
We use resonant soft x-ray scattering (RSXS) to quantify the hole distribution in a superlattice of insulating La2CuO4 (LCO) and overdoped La2-xSrxCuO4 (LSCO). Despite its nonsuperconducting constituents, this structure is superconducting with T_{c}=38 K. found that conducting holes redistribute electronically from LSCO LCO layers. The layers were be optimally doped, suggesting they are main drivers superconductivity. Our results demonstrate utility RSXS for separating electronic structural...
The absorption of light by materials proceeds through the formation excitons, which are states in an excited electron is bound to valence hole it vacated. Understanding structure and dynamics excitons important, for example, developing technologies light-emitting diodes or solar energy conversion. However, there has never been experimental means study time-dependent directly. Here, we use causality-inverted inelastic x-ray scattering (IXS) image charge-transfer exciton prototype insulator...
Multiferroicity in LiCu2O2 single crystals is studied using resonant soft x-ray magnetic scattering, hard diffraction, heat capacity, susceptibility, and electrical polarization. Two transitions are found at 24.6 K (T1) 23.2K (T2). Our data consistent with a sinusoidal spin structure T2<T<T1 helicoidal T<T2, giving rise to ferroelectricity. Surprisingly, above T2, the correlation lengths of structures increase as temperature increases dramatic changes ∼42% occurring along c axis.
The distribution of holes in ${\mathrm{Sr}}_{14\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ is revisited with semiempirical reanalysis the x-ray absorption data and exact diagonalization cluster calculations. Another interpretation XAS leads to much larger ladder hole densities than previously suggested. These new lead a simple Wigner crystal recently reported $1∕3$ $1∕5$ wave vectors along ladder. Our consistent paired rung ladders. Exact results for minimal model...
The superconducting transition temperature ${T}_{c}$ of multilayers electron-doped cuprates, composed underdoped (or undoped) and overdoped La${}_{2\ensuremath{-}x}$Ce${}_{x}$CuO${}_{4}$ (LCCO) Pr${}_{2\ensuremath{-}x}$Ce${}_{x}$CuO${}_{4}$ (PCCO) thin films, is found to increase significantly with respect the corresponding single-phase films. By investigating critical current density superlattices different doping levels layer thicknesses, we find that enhancement caused by a redistribution...
We investigated the orbital and antiferromagnetic ordering behaviors of half-doped bilayer manganite La(2-2x)Sr(1+2x)Mn2O7 (x ≃ 0.5) by using Mn L(2,3)-edge resonant soft x-ray scattering. Resonant scattering reveals CE-type order below T(oo) 220 K, which shows partial melting behavior T(m) 165 K. also found coexistence CE- A-type orders. Both orders involve with nearly same character are coupled each other. These results manifest that ground state is easily susceptible to destabilization...
We used resonant soft x-ray scattering to study the chain ordering in ${\mathrm{Sr}}_{14}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ (SCO). observed, for first time, both and ladder orders SCO with same probe. found that modulation is incommensurate wave vector ${L}_{c}=0.318$, strongly temperature ($T$) dependent, accompanied by a substantial hole modulation. By contrast, hole-depleted control sample ${\mathrm{La}}_{6}{\mathrm{Ca}}_{8}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ was commensurate...
We report on using high-resolution angle-resolved two-photon photoemission to observe a one-dimensional surface state 0.27 eV below the Fermi level stepped Cu(111) surface. The is dispersive along step direction but localized perpendicular orientation. origin of may be explained by confinement due step-edge potential.
Recent scanning-tunneling spectroscopy (STS) studies of the cupric oxychloride ${\mathrm{Na}}_{x}{\mathrm{Ca}}_{2\ensuremath{-}x}\mathrm{Cu}{\mathrm{O}}_{2}{\mathrm{Cl}}_{2}$ (NCCOC) have uncovered a periodic $4a\ifmmode\times\else\texttimes\fi{}4a$ density states (DOS) modulation, termed ``checkerboard'' [T. Hanaguri et al., Nature (London) 430, 1001 (2004)]. The periodicity this phase is same as that ``stripe'' charge order observed with neutron scattering in very similar systems...
Resonant soft x-ray absorption measurements at the O K edge on a SrMnO3/LaMnO3 superlattice show shoulder energy of doped holes, which corresponds to main peak resonant scattering from modulation in hole density. Scattering line shape Mn L3,2 edges has strong variation below ferromagnetic transition temperature. This period equal half superperiod and follows development moment, pointing phase developing interfaces. It occurs energies for Mn3+ Mn4+ valences. A model these observations is...
All-optical switching by domain wall motion has been obtained in Co/Pd superlattices with a TiS oscillator. Heat accumulation is part of the process for our experimental conditions. Numerical calculations point to connection between and in-plane heat diffusion.
Angle-resolved ultrafast two-photon-photoemission is used to investigate image-state-electron lifetimes on two bimetallic surfaces, $\mathrm{Ag}∕\mathrm{Pt}(111)$ and $\mathrm{Ag}∕\mathrm{Pt}(997)$. This photoemission probe measures the relative dependence of image-electron dynamics parallel electron momentum, ${k}_{\ensuremath{\Vert}}$, for flat stepped surfaces. The $n=1$ $n=2$ image states are identified by their ${k}_{\ensuremath{\Vert}}$-dependent energy values surface directions...
X-ray absorption in $\rm Sr_{2}CuO_{4-\delta}-La_{2}CuO_4$ (SCO-LCO) superlattices shows a variable occupation with doping of hole state different from holes doped for $x \lesssim x_{optimal}$ bulk La_{2-x}Sr_{x}CuO_4$ and suggests that this is on apical oxygen atoms polarized the $a-b$ plane. Considering surface reflectivity gives good qualitative description line shapes resonant soft scattering. The interference between superlattice reflections was used to distinguish scatterers SCO LCO...
Pump-probe experiments and polarizing microscopy are applied to examine temperature heat flow in metallic magnetic superlattices on glass substrates. A model of diffusion thin layers for cylindrical symmetry, equivalent the Green's function method, gives a good description results. The frequency dependence modulation shows that layer should be added sample structure. demagnetization patterns reproduced with includes an interface conductance.
We investigate the lateral motion of image-state electrons on two different bimetallic surfaces by using angle-resolved two-photon photoemission. To provide a clear, benchmarked system, measurements are first made flat Ag/Pt(111) and Ag/Ni(111). Two stepped metallic Ag/Pt(997) Ag/Ni(977) then studied; comparison results allows study behavior image Ag regions in presence degrees step regularity. In both systems measurement energy dispersion for moving direction perpendicular to steps shows...
A model of demagnetizing fields and micromagnetic simulations are applied to examine the evolution a demagnetized cylinder. In addition three expected final magnetic structures, fourth switched state is obtained over range energy densities. The absent when neglected. connection all-optical switching materials with perpendicular anisotropy discussed.
Time-resolved pump-probe measurements were made at variable heat accumulation in Co/Pd superlattices. Heat increases the baseline temperature and decreases equilibrium magnetization. Transient ultrafast demagnetization first develops with higher fluence parallel strong thermal spin fluctuations. The is then gradually removed as approaches Curie temperature. transient magnetization time-dependence well fit spin-flip scattering model.
Resonant soft x-ray scattering on complex oxide superlattices shows very large variations in the superlattice reflection position and intensity near La M5,4 edges. dispersion of form factor describes observations well. We determine average density resonant atoms thickness layers.
X-ray absorption spectroscopy and resonant soft x-ray reflectivity show a non-uniform distribution of oxygen holes in La2NiO4 - La2CuO4 (LNO-LCO) superlattice, with excess concentrated the LNO layers. Weak ferromagnetism Tc = 160 K suggests coordinated tilting NiO6 octahedra, similar to that bulk LNO. Ni d3z2-r2 orbitals within layers have spatially variable occupation. This variation valence near LNO-LCO interfaces is observed at L edge, reflection suppressed by symmetry structure, possible...