55 research outputs found
Spin-Orbit-Induced Orbital Excitations in Sr2RuO4 and Ca2RuO4: A Resonant Inelastic X-ray Scattering Study
High-resolution resonant inelastic X-ray scattering (RIXS) at the oxygen
K-edge has been used to study the orbital excitations of Ca2RuO4 and Sr2RuO4.
In combination with linear dichroism X-ray absorption spectroscopy, the
ruthenium 4d-orbital occupation and excitations were probed through their
hybridization with the oxygen p-orbitals. These results are described within a
minimal model, taking into account crystal field splitting and a spin-orbit
coupling \lambda_{so}=200~meV. The effects of spin-orbit interaction on the
electronic structure and implications for the Mott and superconducting ground
states of (Ca,Sr)2RuO4 are discussed.Comment: accepted in PRB 201
Decoupling carrier concentration and electron-phonon coupling in oxide heterostructures observed with resonant inelastic x-ray scattering
We report the observation of multiple phonon satellite features in ultra thin
superlattices of form SrIrO/SrTiO using resonant inelastic x-ray
scattering. As the values of and vary the energy loss spectra show a
systematic evolution in the relative intensity of the phonon satellites. Using
a closed-form solution for the cross section, we extract the variation in the
electron-phonon coupling strength as a function of and . Combined with
the negligible carrier doping into the SrTiO layers, these results indicate
that tuning of the electron-phonon coupling can be effectively decoupled from
doping. This work showcases both a feasible method to extract the
electron-phonon coupling in superlattices and unveils a potential route for
tuning this coupling which is often associated with superconductivity in
SrTiO-based systems.Comment: 4 pages, 5 figure
Description of resonant inelastic x-ray scattering in correlated metals
To fully capitalize on the potential and versatility of resonant inelastic
x-ray scattering (RIXS), it is essential to develop the capability to interpret
different RIXS contributions through calculations, including the dependence on
momentum transfer, from first-principles for correlated materials. Toward that
objective, we present new methodology for calculating the full RIXS response of
a correlated metal in an unbiased fashion. Through comparison of measurements
and calculations that tune the incident photon energy over a wide portion of
the Fe L absorption resonance of the example material BaFeAs, we
show that the RIXS response in BaFeAs is dominated by the direct
channel contribution, including the Raman-like response below threshold, which
we explain as a consequence of the finite core-hole lifetime broadening.
Calculations are initially performed within the first-principles Bethe-Salpeter
framework, which we then significantly improve by convolution with an effective
spectral function for the intermediate-state excitation. We construct this
spectral function, also from first-principles, by employing the cumulant
expansion of the Green's function and performing a real-time time dependent
density functional theory calculation of the response of the electronic system
to the perturbation of the intermediate-state excitation. Importantly, this
allows us to evaluate the indirect RIXS response from first-principles,
accounting for the full periodicity of the crystal structure and with
dependence on the momentum transfer.Comment: 18 pages, submitte
Charge ordering in Ir dimers in the ground state of BaAlIrO
It has been well established experimentally that the interplay of electronic
correlations and spin-orbit interactions in Ir and Ir oxides
results in insulating J=1/2 and J=0 ground states,
respectively. However, in compounds where the structural dimerization of iridum
ions is favourable, the direct Ir -- hybridisation can be significant and
takes a key role. Here, we investigate the effects of direct Ir --
hybridisation in comparison with electronic correlations and spin-orbit
coupling in BaAlIrO, a compound with Ir dimers. Using a
combination of many-body wave function quantum chemistry
calculations and resonant inelastic X-ray scattering (RIXS) experiments, we
elucidate the electronic structure of BaAlIrO. We find excellent
agreement between the calculated and the measured spin-orbit excitations.
Contrary to the expectations, the analysis of the many-body wave function shows
that the two Ir (Ir and Ir) ions in the IrO dimer unit in
this compound preserve their local J character close to 1/2 and 0,
respectively. The local point group symmetry at each of the Ir sites assumes an
important role, significantly limiting the direct -- hybridisation. Our
results emphasize that minute details in the local crystal field (CF)
environment can lead to dramatic differences in electronic states in iridates
and 5 oxides in general.Comment: 5 pages with 3 figure
Damped spin excitations in a doped cuprate superconductor with orbital hybridization
A resonant inelastic x-ray scattering study of overdamped spin excitations in slightly underdoped La2−x Srx CuO4 (LSCO) with x = 0.12 and 0.145 is presented. Three high-symmetry directions have been investigated: (1) the antinodal (0,0) → ( 1 ,0), (2) the nodal (0,0) → ( 1 , 1 ), and (3) the zone-boundary direction
2 4 4 ( 1 1 1 2 ,0) → ( 4 ,4 ) connecting these two. The overdamped excitations exhibit strong dispersions along (1) and (3), whereas a much more modest dispersion is found along (2). This is in strong contrast to the undoped compound
La2CuO4 (LCO) for which the strongest dispersions are found along (1) and (2). The t − t i − t ii − U Hubbard model used to explain the excitation spectrum of LCO predicts—for constant U/t —that the dispersion along (3) scales with (t i/t )2. However, the diagonal hopping t i extracted on LSCO using single-band models is low (t i/t ∼ −0.16) and decreasing with doping. We therefore invoked a two-orbital (dx2 −y2 and dz2 ) model which implies that t i is enhanced. This effect acts to enhance the zone-boundary dispersion within the Hubbard model. We thus conclude that hybridization of dx2 −y2 and dz2 states has a significant impact on the zone-boundary dispersion in LSCO
Orbital dynamics during an ultrafast insulator to metal transition
Phase transitions driven by ultrashort laser pulses have attracted interest
both for understanding the fundamental physics of phase transitions and for
potential new data storage or device applications. In many cases these
transitions involve transient states that are different from those seen in
equilibrium. To understand the microscopic properties of these states, it is
useful to develop elementally selective probing techniques that operate in the
time domain. Here we show fs-time-resolved measurements of V Ledge Resonant
Inelastic X-Ray Scattering (RIXS) from the insulating phase of the Mott-
Hubbard material V2O3 after ultrafast laser excitation. The probed orbital
excitations within the d-shell of the V ion show a sub-ps time response, which
evolve at later times to a state that appears electronically indistinguishable
from the high-temperature metallic state. Our results demonstrate the potential
for RIXS spectroscopy to study the ultrafast orbital dynamics in strongly
correlated materials.Comment: 12 pages, 4 figure
Compatibility of quantitative X-ray spectroscopy with continuous distribution models of water at ambient conditions
The phase diagram of water harbors controversial views on underlying structural properties of its constituting molecular moieties, its fluctuating hydrogen-bonding network, as well as pair-correlation functions. In this work, long energy-range detection of the X-ray absorption allows us to unambiguously calibrate the spectra for water gas, liquid, and ice by the experimental atomic ionization cross-section. In liquid water, we extract the mean value of 1.74 +/- 2.1% donated and accepted hydrogen bonds per molecule, pointing to a continuous-distribution model. In addition, resonant inelastic X-ray scattering with unprecedented energy resolution also supports continuous distribution of molecular neighborhoods within liquid water, as do X-ray emission spectra once the femtosecond scattering duration and proton dynamics in resonant X-ray-matter interaction are taken into account. Thus, X-ray spectra of liquid water in ambient conditions can be understood without a two-structure model, whereas the occurrence of nanoscale-length correlations within the continuous distribution remains open
Probing hydrogen bond strength in liquid water by resonant inelastic X-ray scattering
Local probes of the electronic ground state are essential for understanding hydrogen bonding in aqueous environments. When tuned to the dissociative core-excited state at the O1s pre-edge of water, resonant inelastic X-ray scattering back to the electronic ground state exhibits a long vibrational progression due to ultrafast nuclear dynamics. We show how the coherent evolution of the OH bonds around the core-excited oxygen provides access to high vibrational levels in liquid water. The OH bonds stretch into the long-range part of the potential energy curve, which makes the X-ray probe more sensitive than infra-red spectroscopy to the local environment. We exploit this property to effectively probe hydrogen bond strength via the distribution of intramolecular OH potentials derived from measurements. In contrast, the dynamical splitting in the spectral feature of the lowest valence-excited state arises from the short-range part of the OH potential curve and is rather insensitive to hydrogen bonding
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