5 research outputs found
Resonant elastic X-ray scattering of antiferromagnetic superstructures in EuPtSi
We report resonant elastic X-ray scattering (REXS) of long-range magnetic
order in EuPtSi, combining different scattering geometries with
full linear polarization analysis to unambiguously identify magnetic scattering
contributions. At low temperatures, EuPtSi stabilizes type A
antiferromagnetism featuring various long-wavelength modulations. For magnetic
fields applied in the hard magnetic basal plane, well-defined regimes of
cycloidal, conical, and fan-like superstructures may be distinguished that
encompass a pocket of commensurate type A order without superstructure. For
magnetic field applied along the easy axis, the phase diagram comprises the
cycloidal and conical superstructures only. Highlighting the power of polarized
REXS, our results reveal a combination of magnetic phases that suggest a highly
unusual competition between antiferromagnetic exchange interactions with
Dzyaloshinsky--Moriya spin--orbit coupling of similar strength
Hidden Charge Order in an Iron Oxide Square-Lattice Compound
Since the discovery of charge disproportionation in the FeO2 square-lattice compound Sr3Fe2O7 by Mössbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained âhiddenâ to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe K-edge resonant x-ray scattering to demonstrate checkerboard charge order in the FeO2 planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on âhidden orderâ in other materials
Electronic structure and lattice dynamics of 1T-VSe: origin of the 3D-CDW
In order to characterize in detail the charge density wave (CDW) transition
of 1-VSe, its electronic structure and lattice dynamics are
comprehensively studied by means of x-ray diffraction, angle resolved
photoemission (ARPES), diffuse and inelastic x-ray scattering (IXS), and
state-of-the-art first principles density functional theory calculations.
Resonant elastic x-ray scattering (REXS) does not show any resonant enhancement
at either V or Se K-edges, indicating that the CDW peak describes a purely
structural modulation of the electronic ordering. ARPES identifies (i) a
pseudogap at TT, which leads to a depletion of the density of states
in the plane at TT, and (ii) anomalies in the electronic
dispersion reflecting a sizable impact of phonons on it. A diffuse scattering
precursor, characteristic of soft phonons, is observed at room temperature (RT)
and leads to the full collapse of the low-energy phonon () with
propagation vector (0.25 0 -0.3) r.l.u. We show that the frequency and
linewidth of this mode are anisotropic in momentum space, reflecting the
momentum dependence of the electron-phonon interaction (EPI), hence
demonstrating that the origin of the CDW is, to a much larger extent, due to
the momentum dependence EPI with a small contribution from nesting. The
pressure dependence of the soft mode remains nearly constant up to
13 GPa at RT, with only a modest softening before the transition to the
high-pressure monoclinic phase. The wide set of experimental data are
well captured by our state-of-the art first-principles anharmonic calculations
with the inclusion of van der Waals (vdW) corrections in the
exchange-correlation functional. The description of the electronics and
dynamics of VSe reported here adds important pieces of information to the
understanding of the electronic modulations of TMDs
Hidden Charge Order in an Iron Oxide Square-Lattice Compound
Since the discovery of charge disproportionation in the FeO2 square-lattice compound Sr3Fe2O7 by Mossbauer spectroscopy more than fifty years ago, the spatial ordering pattern of the disproportionated charges has remained "hidden" to conventional diffraction probes, despite numerous x-ray and neutron scattering studies. We have used neutron Larmor diffraction and Fe K-edge resonant x-ray scattering to demonstrate checkerboard charge order in the FeO2 planes that vanishes at a sharp second-order phase transition upon heating above 332 K. Stacking disorder of the checkerboard pattern due to frustrated interlayer interactions broadens the corresponding superstructure reflections and greatly reduces their amplitude, thus explaining the difficulty of detecting them by conventional probes. We discuss the implications of these findings for research on "hidden order" in other materials
Electronic structure and lattice dynamics of 1T-VSe2:Origin of the three-dimensional charge density wave
To characterize in detail the charge density wave (CDW) transition of 1T-VSe2, its electronic structure and lattice dynamics are comprehensively studied by means of x-ray diffraction, muon spectroscopy, angle resolved photoemission (ARPES), diffuse and inelastic x-ray scattering, and state-of-the-art first-principles density functional theory calculations. Resonant elastic x-ray scattering does not show any resonant enhancement at either V or Se, indicating that the CDW peak at the K edges describes a purely structural modulation of the electronic ordering. ARPES experiments identify (i) a pseudogap at T>T-CDW, which leads to a depletion of the density of states in the ML-M'L' plane at