104 research outputs found
Experimental determination of the state-dependent enhancement of the electron-positron momentum density in solids
The state-dependence of the enhancement of the electron-positron momentum
density is investigated for some transition and simple metals (Cr, V, Ag and
Al). Quantitative comparison with linearized muffin-tin orbital calculations of
the corresponding quantity in the first Brillouin zone is shown to yield a
measurement of the enhancement of the s, p and d states, independent of any
parameterizations in terms of the electron density local to the positron. An
empirical correction that can be applied to a first-principles state-dependent
model is proposed that reproduces the measured state-dependence very well,
yielding a general, predictive model for the enhancement of the momentum
distribution of positron annihilation measurements, including those of angular
correlation and coincidence Doppler broadening techniques
Enhanced electron correlations at the SrxCa1-xVO3 surface
We report hard x-ray photoemission spectroscopy measurements of the
electronic structure of the prototypical correlated oxide SrxCa1-xVO3. By
comparing spectra recorded at different excitation energies, we show that 2.2
keV photoelectrons contain a substantial surface component, whereas 4.2 keV
photoelectrons originate essentially from the bulk of the sample.
Bulk-sensitive measurements of the O 2p valence band are found to be in good
agreement with ab initio calculations of the electronic structure, with some
modest adjustments to the orbital-dependent photoionization cross sections. The
evolution of the O 2p electronic structure as a function of the Sr content is
dominated by A-site hybridization. Near the Fermi level, the correlated V 3d
Hubbard bands are found to evolve in both binding energy and spectral weight as
a function of distance from the vacuum interface, revealing higher correlation
at the surface than in the bulk
Fermi surface of an important nano-sized metastable phase: AlLi
Nanoscale particles embedded in a metallic matrix are of considerable
interest as a route towards identifying and tailoring material properties. We
present a detailed investigation of the electronic structure, and in particular
the Fermi surface, of a nanoscale phase ( AlLi) that has so far been
inaccessible with conventional techniques, despite playing a key role in
determining the favorable material properties of the alloy (Al\nobreakdash-9
at. %\nobreakdash-Li). The ordered precipitates only form within the
stabilizing Al matrix and do not exist in the bulk; here, we take advantage of
the strong positron affinity of Li to directly probe the Fermi surface of
AlLi. Through comparison with band structure calculations, we demonstrate
that the positron uniquely probes these precipitates, and present a 'tuned'
Fermi surface for this elusive phase
The electronic structure of {\em R}NiC intermetallic compounds
First-principles calculations of the electronic structure of members of the
NiC series are presented, and their Fermi surfaces investigated for
nesting propensities which might be linked to the charge-density waves
exhibited by certain members of the series ( = Sm, Gd and Nd). Calculations
of the generalized susceptibility, , show strong
peaks at the same -vector in both the real and imaginary parts for
these compounds. Moreover, this peak occurs at a wavevector which is very close
to that experimentally observed in SmNiC. In contrast, for LaNiC (which
is a superconductor below 2.7K) as well as for ferromagnetic SmNiC, there
is no such sharp peak. This could explain the absence of a charge-density wave
transition in the former, and the destruction of the charge-density wave that
has been observed to accompany the onset of ferromagnetic order in the latter.Comment: 5 pages, 7 figures. Accepted for publication in Phys. Rev.
Maximum entropy deconvolution of resonant inelastic x-ray scattering spectra
Resonant inelastic x-ray scattering (RIXS) has become a powerful tool in the
study of the electronic structure of condensed matter. Although the linewidths
of many RIXS features are narrow, the experimental broadening can often hamper
the identification of spectral features. Here, we show that the Maximum Entropy
technique can successfully be applied in the deconvolution of RIXS spectra,
improving the interpretation of the loss features without a severe increase in
the noise ratio
Observation of surface states on heavily indium doped SnTe(111), a superconducting topological crystalline insulator
The topological crystalline insulator tin telluride is known to host
superconductivity when doped with indium (SnInTe), and for low
indium contents () it is known that the topological surface states are
preserved. Here we present the growth, characterization and angle resolved
photoemission spectroscopy analysis of samples with much heavier In doping (up
to ), a regime where the superconducting temperature is increased
nearly fourfold. We demonstrate that despite strong p-type doping, Dirac-like
surface states persist
Direct Observation of Decoupled Structural and Electronic Transitions and an Ambient Pressure Monoclinic-Like Metallic Phase of VO
We report the simultaneous measurement of the structural and electronic
components of the metal-insulator transition of VO using electron and
photoelectron spectroscopies and microscopies. We show that these evolve over
different temperature scales, and are separated by an unusual monoclinic-like
metallic phase. Our results provide conclusive evidence that the new
monoclinic-like metallic phase, recently identified in high-pressure and
nonequilibrium measurements, is accessible in the thermodynamic transition at
ambient pressure, and we discuss the implications of these observations on the
nature of the MIT in VO
Coastal connectivity and spatial subsidy from a microbial perspective
© 2016 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd. The transfer of organic material from one coastal environment to another can increase production in recipient habitats in a process known as spatial subsidy. Microorganisms drive the generation, transformation, and uptake of organic material in shallow coastal environments, but their significance in connecting coastal habitats through spatial subsidies has received limited attention. We address this by presenting a conceptual model of coastal connectivity that focuses on the flow of microbially mediated organic material in key coastal habitats. Our model suggests that it is not the difference in generation rates of organic material between coastal habitats but the amount of organic material assimilated into microbial biomass and respiration that determines the amount of material that can be exported from one coastal environment to another. Further, the flow of organic material across coastal habitats is sensitive to environmental change as this can alter microbial remineralization and respiration rates. Our model highlights microorganisms as an integral part of coastal connectivity and emphasizes the importance of including a microbial perspective in coastal connectivity studies
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