79 research outputs found
Study on the reflectivity properties of spherically bent analyser crystals
Corrigendum (J. Synchrotron Rad. - 2017 : 24, 545-546). DOI: 10.1107/S1600577516019287.Peer reviewe
Experimental Determination of Momentum-Resolved Electron-Phonon Coupling
We provide a novel experimental method to quantitatively estimate the
electron-phonon coupling and its momentum dependence from resonant inelastic
x-ray scattering (RIXS) spectra based on the detuning of the incident photon
energy away from an absorption resonance. We apply it to the cuprate parent
compound NdBaCuO and find that the electronic coupling to the
oxygen half-breathing phonon mode is strongest at the Brillouin zone boundary,
where it amounts to eV, in agreement with previous studies. In
principle, this method is applicable to any absorption resonance suitable for
RIXS measurements and will help to define the contribution of lattice
vibrations to the peculiar properties of quantum materials.Comment: 6 pages, 3 figure
Anisotropic exchange and spin-wave damping in pure and electron-doped SrIrO
The collective magnetic excitations in the spin-orbit Mott insulator
(SrLa)IrO () were investigated by
means of resonant inelastic x-ray scattering. We report significant magnon
energy gaps at both the crystallographic and antiferromagnetic zone centers at
all doping levels, along with a remarkably pronounced momentum-dependent
lifetime broadening. The spin-wave gap is accounted for by a significant
anisotropy in the interactions between isospins, thus
marking the departure of SrIrO from the essentially isotropic
Heisenberg model appropriate for the superconducting cuprates.Comment: 6 pages, 4 figure
Evolution of the magnetic excitations in NaOsO through its metal-insulator transition
The temperature dependence of the excitation spectrum in NaOsO
through its metal-to-insulator transition (MIT) at 410 K has been investigated
using resonant inelastic X-ray scattering (RIXS) at the Os L edge.
High resolution ( 56 meV) measurements show that the
well-defined, low energy magnons in the insulating state weaken and dampen upon
approaching the metallic state. Concomitantly, a broad continuum of excitations
develops which is well described by the magnetic fluctuations of a nearly
antiferromagnetic Fermi liquid. By revealing the continuous evolution of the
magnetic quasiparticle spectrum as it changes its character from itinerant to
localized, our results provide unprecedented insight into the nature of the MIT
in NaOsO.Comment: Accepted in Physical Review Letters, part of a joint submission to
Physical Review B. Supersedes arXiv:1707.0555
Charge response function probed by resonant inelastic x-ray scattering: the signature of electronic gaps of YBaCuO
In strongly correlated systems the complete determination of the dynamical
susceptibility is of special relevance because of
the entwinement of the spin and charge components. Although Resonant Inelastic
X-Ray Scattering (RIXS) spectra are directly related to both the charge
() and the spin ()
contributions, only the latter has been extensively studied with RIXS so far.
Here we show how to extract from RIXS spectra of high- superconducting
cuprates relevant properties of , such as the presence of the
superconducting gap and of the pseudogap. In particular, we exploit the
temperature dependence of the Cu L edge RIXS spectra of underdoped
YBaCuO at specific wave-vectors q. The signature of the
two gaps is in the departure of the low energy Bosonic excitation continuum
from the statistical temperature-dependence. This approach can be immediately
used to investigate systematically the nature of the pseudogap in cuprates,
thereby taking advantage of the RIXS technique that does not suffer the
limitations of surface-sensitive electron spectroscopies. Its extension to
other interesting materials is foreseen.Comment: 11 pages, 9 figure
Fractional Spin Excitations in the Infinite-Layer Cuprate CaCuO2
We use resonant inelastic x-ray scattering (RIXS) to investigate the magnetic dynamics of the infinite-layer cuprate CaCuO2. We find that close to the (1/2,0) point, the single magnon decays into a broad continuum of excitations accounting for about 80% of the total magnetic spectral weight. Polarization-resolved RIXS spectra reveal the overwhelming dominance of the spin-flip (Delta S = 1) character of this continuum with respect to the Delta S = 0 multimagnon contributions. Moreover, its incident-energy dependence is identical to that of the magnon, supporting a common physical origin. We propose that the continuum originates from the decay of the magnon into spinon pairs, and we relate it to the exceptionally high ring exchange J(c) similar to J(1) of CaCuO2. In the infinite-layer cuprates, long-range and multisite hopping integrals are very important, and they amplify the 2D quantum magnetism effects in spite of the 3D antiferromagnetic Neel order
A pseudospinon continuum in CaIrO
In so-called systems, including some iridates and
ruthenates, the coherent superposition of orbitals in the
ground state gives rise to hopping processes that strongly depend on the bond
geometry. Resonant inelastic x-ray scattering (RIXS) measurements on CaIrO
reveal a prototypical pseudospinon continuum, a hallmark
of one-dimensional (1D) magnetic systems despite its three-dimensional crystal
structure. The experimental spectra compare very well to the calculated
magnetic dynamical structure factor of weakly coupled spin-1/2 chains. We
attribute the onset of such quasi-1D magnetism to the fundamental difference in
the magnetic interactions between the pseudospins along
the corner- and edge-sharing bonds in CaIrO.Comment: 8 pages, 4 figure
Structural, Electronic and Magnetic Properties of a Few Nanometer-Thick Superconducting NdBa₂Cu₃O₇ Films
Abstract: Epitaxial films of high critical temperature (Tc) cuprate superconductors preserve
their transport properties even when their thickness is reduced to a few nanometers. However,
when approaching the single crystalline unit cell (u.c.) of thickness, Tc decreases and eventually,
superconductivity is lost. Strain originating from the mismatch with the substrate, electronic
reconstruction at the interface and alteration of the chemical composition and of doping can be
the cause of such changes. Here, we use resonant inelastic x-ray scattering at the Cu L3 edge to study
the crystal field and spin excitations of NdBa2Cu3O7x ultrathin films grown on SrTiO3, comparing
1, 2 and 80 u.c.-thick samples. We find that even at extremely low thicknesses, the strength of the
in-plane superexchange interaction is mostly preserved, with just a slight decrease in the 1 u.c. with
respect to the 80 u.c.-thick sample. We also observe spectroscopic signatures for a decrease of the
hole-doping at low thickness, consistent with the expansion of the c-axis lattice parameter and oxygen
deficiency in the chains of the first unit cell, determined by high-resolution transmission microscopy
and x-ray diffraction
Mobile orbitons in CaCuO: crucial role of the Hund's exchange
We investigate the Cu edge resonant inelastic x-ray scattering (RIXS)
spectra of a quasi-1D antiferromagnet CaCuO. In addition to the
magnetic excitations, which are well-described by the two-spinon continuum, we
observe two dispersive orbital excitations, the and the
orbitons. We carry out a quantitative comparison of the RIXS spectra, obtained
with two distinct incident polarizations, with a theoretical model. We show
that any realistic spin-orbital model needs to include a finite, but realistic,
Hund's exchange eV. Its main effect is an increase in orbiton
velocities, so that their theoretically calculated values match those observed
experimentally. Even though Hund's exchange also mediates some interaction
between spinon and orbiton, the picture of spin-orbit separation remains intact
and describes orbiton motion in this compound.Comment: 13 pages, 10 figure
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