258 research outputs found
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
cannot only be used to investigate single crystalline materials. This method
also enables 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
Magnetic domain fluctuations in an antiferromagnetic film observed with coherent resonant soft x-ray scattering
We report the direct observation of slow fluctuations of helical
antiferromagnetic domains in an ultra-thin holmium film using coherent resonant
magnetic x-ray scattering. We observe a gradual increase of the fluctuations in
the speckle pattern with increasing temperature, while at the same time a
static contribution to the speckle pattern remains. This finding indicates that
domain-wall fluctuations occur over a large range of time scales. We ascribe
this non-ergodic behavior to the strong dependence of the fluctuation rate on
the local thickness of the film.Comment: to appear in Phys. Rev. Let
A Comparison of Stripe Modulations in LaBaCuO and LaNdSrCuO
We report combined soft and hard x-ray scattering studies of the electronic
and lattice modulations associated with stripe order in
LaBaCuO and LaNdSrCuO. We
find that the amplitude of both the electronic modulation of the hole density
and the strain modulation of the lattice is significantly larger in
LaBaCuO than in LaNdSrCuO
and is also better correlated. The in-plane correlation lengths are isotropic
in each case; for LaBaCuO, \AA\
whereas for LaNdSrCuOF,
\AA. We find that the modulations are temperature independent in
LaBaCuO in the low temperature tetragonal phase. In
contrast, in LaNdSrCuO, the amplitude grows
smoothly from zero, beginning 13 K below the LTT phase transition. We speculate
that the reduced average tilt angle in LaBaCuO results
in reduced charge localization and incoherent pinning, leading to the longer
correlation length and enhanced periodic modulation amplitude.Comment: 6 pages, 4 figure
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.
Momentum-dependent charge correlations in YBaCuO superconductors probed by resonant x-ray scattering: Evidence for three competing phases
We have used resonant x-ray scattering to determine the momentum dependent
charge correlations in YBaCuO samples with highly ordered
chain arrays of oxygen acceptors (ortho-II structure). The results reveal
nearly critical, biaxial charge density wave (CDW) correlations at in-plane
wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity
exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length
are enhanced as superconductivity is weakened by an external magnetic field.
Analogous experiments were carried out on a YBaCuO crystal with
a dilute concentration of spinless (Zn) impurities, which had earlier been
shown to nucleate incommensurate magnetic order. Compared to pristine crystals
with the same doping level, the CDW amplitude and correlation length were found
to be strongly reduced. These results indicate a three-phase competition
between spin-modulated, charge-modulated, and superconducting states in
underdoped YBaCuO.Comment: 6 pages, 3 figures revised version, to appear in Phys. Rev. Let
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
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