310 research outputs found
Bimagnon studies in cuprates with Resonant Inelastic X-ray Scattering at the O K edge. II - The doping effect in La2-xSrxCuO4
We present RIXS data at O K edge from La2-xSrxCuO4 vs. doping between x=0.10
and x=0.22 with attention to the magnetic excitations in the Mid-Infrared
region. The sampling done by RIXS is the same as in the undoped cuprates
provided the excitation is at the first pre-peak induced by doping. Note that
this excitation energy is about 1.5 eV lower than that needed to see bimagnons
in the parent compound. This approach allows the study of the upper region of
the bimagnon continuum around 450 meV within about one third of the Brilluoin
Zone around \Gamma. The results show the presence of damped bimagnons and of
higher even order spin excitations with almost constant spectral weight at all
the dopings explored here. The implications on high Tc studies are briefly
addressed
Possibility to realize spin-orbit-induced correlated physics in iridium fluorides
Recent theoretical predictions of "unprecedented proximity" of the electronic
ground state of iridium fluorides to the SU(2) symmetric
limit, relevant for superconductivity in iridates, motivated us to investigate
their crystal and electronic structure. To this aim, we performed
high-resolution x-ray powder diffraction, Ir L-edge resonant inelastic
x-ray scattering, and quantum chemical calculations on Rb[IrF] and
other iridium fluorides. Our results are consistent with the Mott insulating
scenario predicted by Birol and Haule [Phys. Rev. Lett. 114, 096403 (2015)],
but we observe a sizable deviation of the state from the
SU(2) symmetric limit. Interactions beyond the first coordination shell of
iridium are negligible, hence the iridium fluorides do not show any magnetic
ordering down to at least 20 K. A larger spin-orbit coupling in iridium
fluorides compared to oxides is ascribed to a reduction of the degree of
covalency, with consequences on the possibility to realize spin-orbit-induced
strongly correlated physics in iridium fluorides
Resonant X-Ray Scattering and the<i> j</i><sub>eff</sub>=1/2 Electronic Ground State in Iridate Perovskites
The resonant x-ray scattering (magnetic elastic, RXMS, and inelastic, RIXS) of Ir4+ at the L2,3 edges relevant to spin-orbit Mott insulators An+1IrnO3n+1 (A=Sr, Ba, etc.) are calculated using a single-ion model which treats the spin-orbit and tetragonal crystal-field terms on an equal footing. Both RXMS and RIXS in the spin-flip channel are found to display a nontrivial dependence on the direction of the magnetic moment, μ. Crucially, we show that for μ in the ab plane, RXMS in the cross-polarized channel at the L2 edge is zero irrespective of the tetragonal crystal field; spin-flip RIXS, relevant to measurements of magnons, behaves reciprocally, being zero at L2 when μ is perpendicular to the ab plane. Our results have important implications for the assignment of a jeff=1/2 ground state on the basis of resonant x-ray experiments
Anisotropic interactions opposing magnetocrystalline anisotropy in SrNiIrO
We report our investigation of the electronic and magnetic excitations of
SrNiIrO by resonant inelastic x-ray scattering at the Ir L edge.
The intra- electronic transitions are analyzed using an atomic model,
including spin-orbit coupling and trigonal distortion of the IrO
octahedron, confronted to {\it ab initio} quantum chemistry calculations. The
Ir spin-orbital entanglement is quantified and its implication on the magnetic
properties, in particular in inducing highly anisotropic magnetic interactions,
is highlighted. These are included in the spin-wave model proposed to account
for the dispersionless magnetic excitation that we observe at 90 meV. By
counterbalancing the strong Ni easy-plane anisotropy that manifests
itself at high temperature, the anisotropy of the interactions finally leads to
the remarkable easy-axis magnetism reported in this material at low
temperature
Doping Evolution of Magnetic Order and Magnetic Excitations in (SrLa)IrO
We use resonant elastic and inelastic X-ray scattering at the Ir- edge
to study the doping-dependent magnetic order, magnetic excitations and
spin-orbit excitons in the electron-doped bilayer iridate
(SrLa)IrO (). With increasing
doping , the three-dimensional long range antiferromagnetic order is
gradually suppressed and evolves into a three-dimensional short range order
from to , followed by a transition to two-dimensional short range
order between and . Following the evolution of the
antiferromagnetic order, the magnetic excitations undergo damping, anisotropic
softening and gap collapse, accompanied by weakly doping-dependent spin-orbit
excitons. Therefore, we conclude that electron doping suppresses the magnetic
anisotropy and interlayer couplings and drives
(SrLa)IrO into a correlated metallic state hosting
two-dimensional short range antiferromagnetic order and strong
antiferromagnetic fluctuations of moments, with
the magnon gap strongly suppressed.Comment: 6 Pages, 3 Figures, with supplementary in Sourc
Temperature dependence of iron local magnetic moment in phase-separated superconducting chalcogenide
We have studied local magnetic moment and electronic phase separation in
superconducting KFeSe by x-ray emission and absorption
spectroscopy. Detailed temperature dependent measurements at the Fe K-edge have
revealed coexisting electronic phases and their correlation with the transport
properties. By cooling down, the local magnetic moment of Fe shows a sharp drop
across the superconducting transition temperature (T) and the coexisting
phases exchange spectral weights with the low spin state gaining intensity at
the expense of the higher spin state. After annealing the sample across the
iron-vacancy order temperature, the system does not recover the initial state
and the spectral weight anomaly at T as well as superconductivity
disappear. The results clearly underline that the coexistence of the low spin
and high spin phases and the transitions between them provide unusual magnetic
fluctuations and have a fundamental role in the superconducting mechanism of
electronically inhomogeneous KFeSe system.Comment: 6 pages, 5 figure
Orbital occupancies and the putative jeff = 1/2 groundstate in Ba2IrO4: a combined oxygen K edge XAS and RIXS study
The nature of the electronic groundstate of Ba2IrO4 has been addressed using
soft X-ray absorption and inelastic scattering techniques in the vicinity of
the oxygen K edge. From the polarization and angular dependence of XAS we
deduce an approximately equal superposition of xy, yz and zx Ir4+ 5d orbitals.
By combining the measured orbital occupancies, with the value of the spin-orbit
coupling provided by RIXS, we estimate the crystal field splitting associated
with the tetragonal distortion of the IrO6 octahedra to be small, \Delta=50(50)
meV. We thus conclude definitively that Ba2IrO4 is a close realization of a
spin-orbit Mott insulator with a jeff = 1/2 groundstate, thereby overcoming
ambiguities in this assignment associated with the interpretation of X-ray
resonant scattering experiments.Comment: 5 pages, 5 figure
Is Parkinson's disease an unique clinical entity? Rigid or tremor dominant PD: Two faces of the same coin
Parkinson's disease is one of the most described neurodegenerative pathologies; though it is one of the most complex pathologies, is not fully understood, correctly identified, with its different types of presentation, its clinical course and the neural networks involved. We report on a series consisting of 432 de novo PD diagnosed patients, and 457 control cases. We identify a possible independent relationship between two clinical PD presentation, akinetic-rigid and tremor-dominant, and cognitive and behavioral changes. A 24-months follow-up allows to identify new information still not fully explored
Charge localization at the interface between La1-xSrxMnO3 and the infinite layers cuprate CaCuO2
(CaCuO2)m/(La0.7Sr0.3MnO3)n superlattices, consisting of the infinite layers
cuprate CaCuO2 and the optimally doped manganite La1-xSrxMnO3, were grown by
pulsed laser deposition. The transport properties are dominated by the
manganite block. X-Ray Absorption spectroscopy measurements show a clear
evidence of an orbital reconstruction at the interface, ascribed to the
hybridization between the Cu 3d3z2-r2 and the Mn 3d3z2-r2 orbitals via
interface apical oxygen ions. Such a mechanism localizes holes at the
interfaces, thus preventing charge transfer to the CaCuO2 block. Some charge
(holes) transfer occurs toward the La0.7Sr0.3MnO3 block in strongly oxidized
superlattices, contributing to the suppression of the magnetotransport
properties.Comment: 20 pages, 6 figure
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