389 research outputs found
Raman and fluorescence contributions to resonant inelastic soft x-ray scattering on LaAlO/SrTiO heterostructures
We present a detailed study of the Ti 3 carriers at the interface of
LaAlO/SrTiO heterostructures by high-resolution resonant inelastic soft
x-ray scattering (RIXS), with special focus on the roles of overlayer thickness
and oxygen vacancies. Our measurements show the existence of interfacial Ti
3 electrons already below the critical thickness for conductivity and an
increase of the total interface charge up to a LaAlO overlayer thickness of
6 unit cells before it levels out. By comparing stoichiometric and oxygen
deficient samples we observe strong Ti 3 charge carrier doping by oxygen
vacancies. The RIXS data combined with photoelectron spectroscopy and transport
measurements indicate the simultaneous presence of localized and itinerant
charge carriers. However, it is demonstrated that the relative amount of
localized and itinerant Ti electrons in the ground state cannot be deduced
from the relative intensities of the Raman and fluorescence peaks in excitation
energy dependent RIXS measurements, in contrast to previous interpretations.
Rather, we attribute the observation of either the Raman or the fluorescence
signal to the spatial extension of the intermediate state reached in the RIXS
excitation process.Comment: 9 pages, 6 figure
High-energy photoemission on Fe3O4: Small polaron physics and the Verwey transition
We have studied the electronic structure and charge ordering (Verwey)
transition of magnetite (Fe3O4) by soft x-ray photoemission. Due to the
enhanced probing depth and the use of different surface preparations we are
able to distinguish surface and volume effects in the spectra. The pseudogap
behavior of the intrinsic spectra and its temperature dependence give evidence
for the existence of strongly bound small polarons consistent with both dc and
optical conductivity. Together with other recent structural and theoretical
results our findings support a picture in which the Verwey transition contains
elements of a cooperative Jahn-Teller effect, stabilized by local Coulomb
interaction
Comparative analysis of tertiary control systems for smart grids using the Flex Street model
Various smart grid control systems have been developed with different architectures. Comparison helps developers identify their strong and weak points. A three-step analysis method is proposed to facilitate the comparison of independently developed control systems. In the first step, a microgrid model is created describing demand and supply patterns of controllable and non-controllable devices (Flex Street). In the second step, a version of Flex Street is used to design a case, with a given control objective and key performance indicators. In the last step, simulations of different control systems are performed and their results are analysed and compared. The Flex Street model describes a diverse set of households based on realistic data. Furthermore, its bottom-up modelling approach makes it a flexible tool for designing cases. Currently, three cases with peak-shaving objectives are developed based on scenarios of the Dutch residential sector, specifying various penetration rates of renewable and controllable devices.
The proposed method is demonstrated by comparing IntelliGator and TRIANA, two independently developed control systems, on peak reduction, energy efficiency, savings and abated emissions. Results show that IntelliGator---a real-time approach---is proficient in reducing peak demand, while TRIANA---a planning approach---also levels intermediate demand. Both systems yield benefits (\geneuro5--54 per household per year) through reduced transport losses and network investments in the distribution network
Surface characterization and surface electronic structure of organic quasi-one-dimensional charge transfer salts
We have thoroughly characterized the surfaces of the organic charge-transfer
salts TTF-TCNQ and (TMTSF)2PF6 which are generally acknowledged as prototypical
examples of one-dimensional conductors. In particular x-ray induced
photoemission spectroscopy turns out to be a valuable non-destructive
diagnostic tool. We show that the observation of generic one-dimensional
signatures in photoemission spectra of the valence band close to the Fermi
level can be strongly affected by surface effects. Especially, great care must
be exercised taking evidence for an unusual one-dimensional many-body state
exclusively from the observation of a pseudogap.Comment: 11 pages, 12 figures, v2: minor changes in text and figure labellin
Remnant Fermi surface in the presence of an underlying instability in layered 1T-TaS_2
We report high resolution angle-scanned photoemission and Fermi surface (FS)
mapping experiments on the layered transition-metal dichalcogenide 1T-TaS_2 in
the quasi commensurate (QC) and the commensurate (C) charge-density-wave (CDW)
phase. Instead of a nesting induced partially removed FS in the CDW phase we
find a pseudogap over large portions of the FS. This remnant FS exhibits the
symmetry of the one-particle normal state FS even when passing from the
QC-phase to the C-phase. Possibly, this Mott localization induced transition
represents the underlying instability responsible for the pseudogapped FS
Microscopic origin of the mobility enhancement at a spinel/perovskite oxide heterointerface revealed by photoemission spectroscopy
The spinel/perovskite heterointerface -AlO/SrTiO hosts a
two-dimensional electron system (2DES) with electron mobilities exceeding those
in its all-perovskite counterpart LaAlO/SrTiO by more than an order of
magnitude despite the abundance of oxygen vacancies which act as electron
donors as well as scattering sites. By means of resonant soft x-ray
photoemission spectroscopy and \textit{ab initio} calculations we reveal the
presence of a sharply localized type of oxygen vacancies at the very interface
due to the local breaking of the perovskite symmetry. We explain the
extraordinarily high mobilities by reduced scattering resulting from the
preferential formation of interfacial oxygen vacancies and spatial separation
of the resulting 2DES in deeper SrTiO layers. Our findings comply with
transport studies and pave the way towards defect engineering at interfaces of
oxides with different crystal structures.Comment: Accepted as Rapid Communications in Physical Review
Non-fermi-liquid single particle lineshape of the quasi-one-dimensional non-CDW metal Li_{0.9}Mo_{6}O_{17} : comparison to the Luttinger liquid
We report the detailed non-Fermi liquid (NFL) lineshape of the dispersing
excitation which defines the Fermi surface (FS) for quasi-one-dimensional
Li_{0.9}Mo_{6}O_{17}. The properties of Li_{0.9}Mo_{6}O_{17} strongly suggest
that the NFL behavior has a purely electronic origin. Relative to the
theoretical Luttinger liquid lineshape, we identify significant similarities,
but also important differences.Comment: 5 pages, 3 eps figure
Genome sequence and characterization of Streptomyces phages Vanseggelen and Verabelle, representing two new species within the genus Camvirus
NWOVI.C.192.002Microbial Biotechnolog
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