75 research outputs found
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
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
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
Determining the Electron-Phonon Coupling in Superconducting Cuprates by Resonant Inelastic X-ray Scattering: Methods and Results on NdBaCuO
The coupling between lattice vibration quanta and valence electrons can
induce charge density modulations and decisively influence the transport
properties of materials, e.g. leading to conventional superconductivity. In
high critical temperature superconductors, where electronic correlation is the
main actor, the actual role of electron-phonon coupling (EPC) is being
intensely debated theoretically and investigated experimentally. We present an
in-depth study of how the EPC strength can be obtained directly from resonant
inelastic x-ray scattering (RIXS) data through the theoretical approach derived
by Ament et al. [EPL 95, 27008 (2011)]. The role of the model parameters (e.g.
phonon energy , intermediate state lifetime , EPC matrix
element , and detuning energy ) is thoroughly analyzed, providing
general relations among them that can be used to make quantitative estimates of
the dimensionless EPC without detailed microscopic
modeling. We then apply these methods to very high resolution Cu edge
RIXS spectra of three NdBaCuO films. For the
insulating antiferromagnetic parent compound the value of as a function of
the in-plane momentum transfer is obtained for Cu-O bond-stretching (breathing)
and bond-bending (buckling) phonon branches. For the underdoped and the nearly
optimally doped samples, the effects of Coulomb screening and of
charge-density-wave correlations on are assessed. In light of the
anticipated further improvements of the RIXS experimental resolution, this work
provides a solid framework for an exhaustive investigation of the EPC in
cuprates and other quantum materials.Comment: 21 pages, 16 figure
Scientific Opinion on an application (Reference EFSA-GMO-NL-2011-100) for the placing on the market of the herbicide-tolerant, increased oleic acid genetically modified soybean MON 87705$ MON 89788 for food and feed uses, import and processing under Regulation (EC) No 1829/2003 from Monsanto
The EFSA GMO Panel previously assessed the two single events combined to produce soybean MON 87705 × MON 89788 and did not identify safety concerns. No new data on the single events affecting the previous conclusions were identified. No differences in composition requiring further assessment were observed between soybean MON 87705 × MON 89788 and its comparator, except for the intended trait i.e. an altered fatty acid profile. Nutritional assessment on soybean MON 87705 × MON 89788 oil and oil-containing food products did not identify concerns on human health and nutrition. There are no concerns regarding the use of feedingstuffs from defatted soybean meal MON 87705 × MON 89788. The EFSA GMO Panel is of the opinion that soybean MON 87705 × MON 89788 is as safe, and at least as nutritious, as its comparator and commercial soybean varieties. There is no reason to expect interactions between the single events that could impact on the food and feed safety and the nutritional properties of soybean MON 87705 × MON 89788. There are no indications of an increased likelihood of establishment and spread of feral soybean plants. Potential interactions with the biotic and abiotic environment were not considered to be a relevant issue. The unlikely but theoretically possible transfer of the recombinant genes from soybean MON 87705 × MON 89788 to environmental bacteria does not give rise to any safety concern. The post-market environmental monitoring plan and reporting intervals are in line with the scope of the application. The EFSA GMO Panel considers that the information available for soybean MON 87705 × MON 89788 addresses the scientific comments raised by Member States. The EFSA GMO Panel concludes, considering the scope of the application, that soybean MON 87705 × MON 89788 is as safe as its comparator and non-GM soybean reference varieties with respect to potential effects on human and animal health and the environment. The GMO Panel recommends a post-market monitoring plan, focusing on import data and, if needed, on consumption data for the European population, for the marketed foods and feed
Guidance for renewal applications of genetically modified food and feed authorised under Regulation (EC) No 1829/2003
Determining the electron-phonon coupling in superconducting cuprates by resonant inelastic x-ray scattering: Methods and results on Nd1+xBa2-xCu3O7-δ
The coupling between lattice vibration quanta and valence electrons can induce charge-density modulations and decisively influence the transport properties of materials, e.g., leading to conventional superconductivity. In high-critical-temperature superconductors, where electronic correlation is the main actor, the actual role of electron-phonon coupling (EPC) is being intensely debated theoretically and investigated experimentally. We present an in-depth study of how the EPC strength can be obtained directly from resonant inelastic x-ray scattering (RIXS) data through the theoretical approach derived by Ament et\ua0al. [Europhys. Lett. 95, 27008 (2011)]. The role of the model parameters (e.g., phonon energy ω0, intermediate state lifetime 1/Γ, EPC matrix element M, and detuning energy Ω) is thoroughly analyzed, providing general relations among them that can be used to make quantitative estimates of the dimensionless EPC g=(M/ω0)2 without detailed microscopic modeling. We then apply these methods to very high-resolution Cu L3-edge RIXS spectra of three Nd1+xBa2−xCu3O7−δ films. For the insulating antiferromagnetic parent compound, the value of M as a function of the in-plane momentum transfer is obtained for Cu-O bond-stretching (breathing) and bond-bending (buckling) phonon branches. For the underdoped and the nearly optimally doped samples, the effects of Coulomb screening and of charge-density-wave correlations on M are assessed. In light of the anticipated further improvements of the RIXS experimental resolution, this work provides a solid framework for an exhaustive investigation of the EPC in cuprates and other quantum materials
Collective nature of orbital excitations in layered cuprates in the absence of apical oxygens
We have investigated the 3d orbital excitations in CaCuO2 (CCO), Nd2CuO4
(NCO) and La2CuO4 (LCO) using high-resolution resonant inelastic x-ray
scattering. In LCO they behave as well-localized excitations, similarly to
several other cuprates. On the contrary, in CCO and NCO the dxy orbital clearly
disperse, pointing to a collective character of this excitation (orbiton) in
compounds without apical oxygen. We ascribe the origin of the dispersion as
stemming from a substantial next-nearest-neighbor (NNN) orbital superexchange.
Such an exchange leads to the liberation of orbiton from its coupling to
magnons, which is associated with the orbiton hopping between nearest neighbor
copper sites. We show that the exceptionally large NNN orbital superexchange
can be traced back to the absence of apical oxygens suppressing the charge
transfer energy.Comment: 18 pages, 7 figure
- …