Resonant elastic soft x-ray scattering

Resonant (elastic) soft x-ray scattering (RSXS) offers a unique element, site and valence specific probe to study spatial modulations of charge, spin and orbital degrees of freedom in solids on the nanoscopic length scale. It is not only used to investigate single-crystalline materials. This method also enables one to examine electronic ordering phenomena in thin films and to zoom into electronic properties emerging at buried interfaces in artificial heterostructures. During the last 20 years, this technique, which combines x-ray scattering with x-ray absorption spectroscopy, has developed into a powerful probe to study electronic ordering phenomena in complex materials and furthermore delivers important information on the electronic structure of condensed matter. This review provides an introduction to the technique, covers the progress in experimental equipment, and gives a survey on recent RSXS studies of ordering in correlated electron systems and at interfaces.

Coherent excitations and electron-phonon coupling in Ba/EuFe2As2 compounds investigated by femtosecond time- and angle-resolved photoemission spectroscopy

We employed femtosecond time- and angle-resolved photoelectron spectroscopy to analyze the response of the electronic structure of the 122 Fe-pnictide parent compounds Ba/EuFe(2)As(2) and optimally doped BaFe(1.85)Co(0.15)As(2) near the Γ point to optical excitation by an infrared femtosecond laser pulse. We identify pronounced changes of the electron population within several 100 meV above and below the Fermi level, which we explain as a combination of (i) coherent lattice vibrations, (ii) a hot electron and hole distribution, and (iii) transient modifications of the chemical potential. The responses of the three different materials are very similar. In the coherent response we identify three modes at 5.6, 3.3, and 2.6 THz. While the highest frequency mode is safely assigned to the A(1g) mode, the other two modes require a discussion in comparison to the literature. Employing a transient three temperature model we deduce from the transient evolution of the electron distribution a rather weak, momentum-averaged electron-phonon coupling quantified by values for λ<ω(2)> between 30 and 70 meV(2). The chemical potential is found to present pronounced transient changes reaching a maximum of 15 meV about 0.6 ps after optical excitation and is modulated by the coherent phonons. This change in the chemical potential is particularly strong in a multiband system like the 122 Fe-pnictide compounds investigated here due to the pronounced variation of the electron density of states close to the equilibrium chemical potential.

Medically refractory neurosarcoidosis treated with infliximab

Neurosarcoidosis can worsen despite standard immunosuppressive therapy, a situation for which there is no established medical management. We present three cases of medically refractory neurosarcoidosis treated with infliximab. All three patients showed a clinical response to this treatment and side effects were limited. A summary of reported cases of neurosarcoidosis treated with infliximab is included. This case series supports a role for infliximab in the treatment of patients with medically refractory neurosarcoidosis.

Ultrafast momentum-dependent response of electrons in antiferromagnetic EuFe2As2 driven by optical excitation

Employing the momentum sensitivity of time- and angle-resolved photoemission spectroscopy we demonstrate the analysis of ultrafast single- and many-particle dynamics in antiferromagnetic EuFe(2)As(2). Their separation is based on a temperature-dependent difference of photoexcited hole and electron relaxation times probing the single-particle band and the spin density wave gap, respectively. Reformation of the magnetic order occurs at 800 fs, which is 4 times slower compared to electron-phonon equilibration due to a smaller spin-dependent relaxation phase space.

Large tunable Rashba spin splitting of a two-dimensional electron gas in Bi2Se3

We report a Rashba spin splitting of a two-dimensional electron gas in the topological insulator Bi(2)Se(3) from angle-resolved photoemission spectroscopy. We further demonstrate its electrostatic control, and show that spin splittings can be achieved which are at least an order-of-magnitude larger than in other semiconductors. Together these results show promise for the miniaturization of spintronic devices to the nanoscale and their operation at room temperature.

Experimental state tomography of itinerant single microwave photons

A wide range of experiments studying microwave photons localized in superconducting cavities have made important contributions to our understanding of the quantum properties of radiation. Propagating microwave photons, however, have so far been studied much less intensely. Here we present measurements in which we reconstruct the quantum state of itinerant single photon Fock states and their superposition with the vacuum by analyzing moments of the measured amplitude distribution up to fourth order. Using linear amplifiers and quadrature amplitude detectors, we have developed efficient methods to separate the detected single photon signal from the noise added by the amplifier. From our measurement data we have also reconstructed the corresponding Wigner function.

Tunable band gap in hydrogenated quasi-free-standing graphene

We show by angle-resolved photoemission spectroscopy that a tunable gap in quasi-free-standing monolayer graphene on Au can be induced by hydrogenation. The size of the gap can be controlled via hydrogen loading and reaches approximately 1.0 eV for a hydrogen coverage of 8%. The local rehybridization from sp(2) to sp(3) in the chemical bonding is observed by X-ray photoelectron spectroscopy and X-ray absorption and allows for a determination of the amount of chemisorbed hydrogen. The hydrogen induced gap formation is completely reversible by annealing without damaging the graphene. Calculations of the hydrogen loading dependent core level binding energies and the spectral function of graphene are in excellent agreement with photoemission experiments. Hydrogenation of graphene gives access to tunable electronic and optical properties and thereby provides a model system to study hydrogen storage in carbon materials.

Strength of correlation effects in the electronic structure of iron

The strength of electronic correlation effects in the spin-dependent electronic structure of ferromagnetic bcc Fe(110) has been investigated by means of spin and angle-resolved photoemission spectroscopy. The experimental results are compared to theoretical calculations within the three-body scattering approximation and within the dynamical mean-field theory, together with one-step model calculations of the photoemission process. This comparison indicates that the present state of the art many-body calculations, although improving the description of correlation effects in Fe, give too small mass renormalizations and scattering rates thus demanding more refined many-body theories including nonlocal fluctuations.

Linear plasmon dispersion in single-wall carbon nanotubes and the collective excitation spectrum of graphene

We have measured a strictly linear pi plasmon dispersion along the axis of individualized single-wall carbon nanotubes, which is completely different from plasmon dispersions of graphite or bundled single-wall carbon nanotubes. Comparative ab initio studies on graphene-based systems allow us to reproduce the different dispersions. This suggests that individualized nanotubes provide viable experimental access to collective electronic excitations of graphene, and it validates the use of graphene to understand electronic excitations of carbon nanotubes. In particular, the calculations reveal that local field effects cause a mixing of electronic transitions, including the "Dirac cone," resulting in the observed linear dispersion.

Optimizing BeLPT criteria for beryllium sensitization

BACKGROUND

The beryllium lymphocyte proliferation test (BeLPT) is used to identify persons sensitized to beryllium. ATSDR convened an expert panel of physicians and scientists in April 2006 to discuss this test and to consider what BeLPT test results actually establish beryllium sensitization. The three criteria proposed by panel members were (1)one abnormal result, (2)one abnormal and one borderline result, and (3)two abnormal results.

METHODS

Complete algorithms were developed for each of the three proposed criteria. Using single-test outcome probabilities developed by Stange et al. [2004. Am J Ind Med 46:453-462], we calculated and compared the sensitivity, specificity, and positive predictive values (PPVs) for each set of criteria.

RESULTS

The overall sensitivity and specificity of the three criteria were similar. When the criteria required confirmation of an abnormal result the PPV was higher--whether the requirement was satisfied by a borderline result, or only by another abnormal result. Confirmation also reduced the likelihood of false positives. The differences between the three criteria decreased as the prevalence of sensitization increased.

CONCLUSIONS

A single unconfirmed abnormal is usually insufficient to establish sensitization for an apparently healthy person. When the prevalence of beryllium sensitization in a group is high, however, even a single abnormal BeLPT can be a strong predictor.

Stimulation of monocytes and macrophages: possible influence of surface roughness

The aim of this study was to understand the mechanisms of interaction of monocytes/macrophages and foreign body giant cell (FBGC) with implant materials, with respect to the roughness and the solubility of calcium phosphate based coatings. Anderson et al. (Bone Engineering, J.E. Davies, ed., Toronto, 2000, pp. 81-93) showed that the presence of FBGC's and monocytes/macrophages influenced the strength of the implant-tissue integration and that more monocytes/macrophages rested on smooth surfaces compared to rough surfaces. We seeded human bone marrow cells on uncoated ultrasmooth polished TiAl6V4 samples as well as on coated TiAl6V4 discs of the same diameter with two different calcium phosphates coatings, monetite (DCP) and hydroxyapatite (OHAp), both with rougher surfaces. On uncoated ultrasmooth polished TiAl6V4 discs (UUTi, diameter 16 mm, thickness 2 mm) and on TiAl6V4 discs of same diameter coated with OHAP or DCPA, human bone marrow cells (HMBC) were seeded and cultivated under standard culture conditions for 90 days without addition of inducing substances like ascorbic acid, Na-beta-glycerophosphate or dexamethasone. The roughnesses of the virgin samples were assessed with atomic force microscopy and light profilometry. After 90 days of cultivation a fraction of the samples, with cells and extracellular matrix, were stained with hematoxylin eosin (HE) and examined in light microscopy. R(a) roughness values of virgin uncoated TiAl6V4 samples were 0.001 microm, of DCP coated discs 4 microm and of OHAp coated discs 3 microm. The examination of HE stained samples showed a high number of FBGC and monocytes/macrophages on the UUTi samples. On the DCP coated samples there were less FBGC and monocytes/macrophages and on the OHAp coated samples we could not find any FBGC and monocytes/macrophages. The extracellular matrix (ECM) we found on the UUTi samples was finer and thinner than on the coated samples. The ECM was vastly spread and not dense on the UUTi samples in contrast to the calcium phosphate coated samples, where the ECM was much thicker and stronger. The ultrasmooth surface of the uncoated TiAl6V4 samples, a material which is accepted to be biocompatible, evidently induced the differentiation of cells of the monocytic lineage and the formation of FBGC out of the cell populations present in the human bone marrow.

Momentum and energy dependence of the anomalous high-energy dispersion in the electronic structure of high temperature superconductors

Using high-resolution angle-resolved photoemission spectroscopy we have studied the momentum and photon energy dependence of the anomalous high-energy dispersion, termed waterfalls, between the Fermi level and 1 eV binding energy in several high-T_{c} superconductors. We observe strong changes of the dispersion between different Brillouin zones and a strong dependence on the photon energy around 75 eV, which we associate with the resonant photoemission at the Cu3p-->3d_{x;{2}-y;{2}} edge. We conclude that the high-energy "waterfall" dispersion results from a strong suppression of the photoemission intensity at the center of the Brillouin zone due to matrix element effects and is, therefore, not an intrinsic feature of the spectral function. This indicates that the new high-energy scale in the electronic structure of cuprates derived from the waterfall-like dispersion may be incorrect.