97 research outputs found
The Temperature Evolution of the Out-of-Plane Correlation Lengths of Charge-Stripe Ordered La(1.725)Sr(0.275)NiO(4)
The temperature dependence of the magnetic order of stripe-ordered
La(1.725)Sr(0.275)NiO(4) is investigated by neutron diffraction. Upon cooling,
the widths if the magnetic Bragg peaks are observed to broaden. The degree of
broadening is found to be very different for l = odd-integer and l =
even-integer magnetic peaks. We argue that the observed behaviour is a result
of competition between magnetic and charge order.Comment: 3 figure
Direct observation of t2g orbital ordering in magnetite
Using soft-x-ray diffraction at the site-specific resonances in the Fe L23
edge, we find clear evidence for orbital and charge ordering in magnetite below
the Verwey transition. The spectra show directly that the (001/2) diffraction
peak (in cubic notation) is caused by t2g orbital ordering at octahedral Fe2+
sites and the (001) by a spatial modulation of the t2g occupation.Comment: to appear in Phys. Rev. Let
Intrinsic and extrinsic x-ray absorption effects in soft x-ray diffraction from the superstructure in magnetite
We studied the (001/2) diffraction peak in the low-temperature phase of
magnetite (Fe3O4) using resonant soft x-ray diffraction (RSXD) at the Fe-L2,3
and O-K resonance. We studied both molecular-beam-epitaxy (MBE) grown thin
films and in-situ cleaved single crystals. From the comparison we have been
able to determine quantitatively the contribution of intrinsic absorption
effects, thereby arriving at a consistent result for the (001/2) diffraction
peak spectrum. Our data also allow for the identification of extrinsic effects,
e.g. for a detailed modeling of the spectra in case a "dead" surface layer is
present that is only absorbing photons but does not contribute to the
scattering signal.Comment: to appear in Phys. Rev.
Evidence for core-hole-mediated inelastic x-ray scattering from metallic FeTe
We present a detailed analysis of resonant inelastic scattering (RIXS) from
FeTe with unprecedented energy resolution. In contrast to the sharp
peaks typically seen in insulating systems at the transition metal edge,
we observe spectra which show different characteristic features. For low energy
transfer, we experimentally observe theoretically predicted many-body effects
of resonant Raman scattering from a non-interacting gas of fermions.
Furthermore, we find that limitations to this many-body electron-only theory
are realized at high Raman shift, where an exponential lineshape reveals an
energy scale not present in these considerations. This regime, identified as
emission, requires considerations of lattice degrees of freedom to understand
the lineshape. We argue that both observations are intrinsic general features
of many-body physics of metals.Comment: 4 pages, 4 figure
Spectroscopy of stripe order in La1.8Sr0.2NiO4 using resonant soft x-ray diffraction
Strong resonant enhancements of the charge-order and spin-order
superstructure-diffraction intensities in La1.8Sr0.2NiO4 are observed when
x-ray energies in the vicinity of the Ni L2,3 absorption edges are used. The
pronounced photon-energy and polarization dependences of these diffraction
intensities allow for a critical determination of the local symmetry of the
ordered spin and charge carriers. We found that not only the antiferromagnetic
order but also the charge-order superstructure resides within the NiO2 layers;
the holes are mainly located on in-plane oxygens surrounding a Ni2+ site with
the spins coupled antiparallel in close analogy to Zhang-Rice singlets in the
cuprates.Comment: 4 pages, 3 figure
Ultrafast electronic processes in an insulator The Be and O sites in BeO
The short time dynamics of amorphous beryllium oxide a BeO has been investigated for electronic excitation ionization by fast incident electrons, as well as by Ar7 , Ar15 , Xe15 , and Xe31 ions at velocities of 6 10 the speed of light. Site specific Auger electron spectra induced by fast heavy ions are the central point of this investigation. Electron induced Auger spectra serve as a reference and electron energy loss EELS spectroscopy as well as resonant inelastic X ray scattering RIXS are invoked for quantitative understanding. For the heavy ion case, we observe strong variations in the corresponding spectral distributions of Be K and O K Auger lines. These are related to local changes of the electron density, of the electron temperature and even of the electronic band structure of BeO on a femtosecond time scale after the passage of highly charged heavy ions
Analysis of charge and orbital order in Fe_{3}O_{4} by Fe L_{2,3} resonant x-ray diffraction
To elucidate charge and orbital order below the Verwey transition temperature
TV∼125 K, a thin layer of magnetite partially detwined by growth on the
stepped MgO(001) substrate has been studied by means of soft x-ray diffraction
at the Fe L2,3 resonance. The azimuth angle, incident photon polarization, and
energy dependence of the (0012)c and (001)c reflection intensities have been
measured, and analyzed using a configuration-interaction FeO6 cluster model.
The azimuth dependence of the (0012)c reflection intensities directly
represents the space-group symmetry of the orbital order in the initial state
rather than indirectly through the intermediate-state level shifts caused by
the order-induced lattice distortions. From the analysis of the (0012)c
reflection intensities, the orbital order in the t2g orbitals of B sites below
TV is proved to have a large monoclinic deformation with the value of
Re[Fxy]/Re[Fyz]∼2. This finding contradicts the majority of theories on the
Verwey transition so far proposed. We show that the experimentally observed
resonance spectra cannot be explained by orbital and charge orders obtained
with recent LDA+U and GGA+U band structure calculations but by a complex-
number orbital order with excellent agreement
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