109 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
Activation of intestinal spinal afferent endings by changes in intra‐mesenteric arterial pressure
Author manuscript made available following 12 month embargo from date of publication (25 June 2015) in accordance with publisher copyright policy.KEY POINTS:
A major class of mechano-nociceptors to the intestine have mechanotransduction sites on extramural and intramural arteries and arterioles ('vascular afferents'). These sensory neurons can be activated by compression or axial stretch of vessels. Using isolated preparations we showed that increasing intra-arterial pressure, within the physiological range, activated mechano-nociceptors on vessels in intact mesenteric arcades, but not in isolated arteries. This suggests that distortion of the branching vascular tree is the mechanical adequate stimulus for these sensory neurons, rather than simple distension. The same rises in pressure also activated intestinal peristalsis in a partially capsaicin-sensitive manner indicating that pressure-sensitive vascular afferents influence enteric circuits. The results identify the mechanical adequate stimulus for a major class of mechano-nociceptors with endings on blood vessels supplying the gut wall; these afferents have similar endings to ones supplying other viscera, striated muscle and dural vessels.
ABSTRACT:
Spinal sensory neurons innervate many large blood vessels throughout the body. Their activation causes the hallmarks of neurogenic inflammation: vasodilatation through the release of the neuropeptide calcitonin gene-related peptide and plasma extravasation via tachykinins. The same vasodilator afferent neurons show mechanical sensitivity, responding to crushing, compression or axial stretch of blood vessels - responses which activate pain pathways and which can be modified by cell damage and inflammation. In the present study, we tested whether spinal afferent axons ending on branching mesenteric arteries ('vascular afferents') are sensitive to increased intravascular pressure. From a holding pressure of 5 mmHg, distension to 20, 40, 60 or 80 mmHg caused graded, slowly adapting increases in firing of vascular afferents. Many of the same afferent units showed responses to axial stretch, which summed with responses evoked by raised pressure. Many vascular afferents were also sensitive to raised temperature, capsaicin and/or local compression with von Frey hairs. However, responses to raised pressure in single, isolated vessels were negligible, suggesting that the adequate stimulus is distortion of the arterial arcade rather than distension per se. Increasing arterial pressure often triggered peristaltic contractions in the neighbouring segment of intestine, an effect that was mimicked by acute exposure to capsaicin (1 μm) and which was reduced after desensitisation to capsaicin. These results indicate that sensory fibres with perivascular endings are sensitive to pressure-induced distortion of branched arteries, in addition to compression and axial stretch, and that they contribute functional inputs to enteric motor circuits
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
Identification of unique release kinetics of serotonin from guinea-pig and human enterochromaffin cells
This is the accepted version of the following article: [Raghupathi, R., Duffield, M. D., Zelkas, L., Meedeniya, A., Brookes, S. J. H., Sia, T. C., Wattchow, D. A., Spencer, N. J. and Keating, D. J. (2013), Identification of unique release kinetics of serotonin from guinea-pig and human enterochromaffin cells. The Journal of Physiology, 591: 5959–5975. doi: 10.1113/jphysiol.2013.259796], which has been published in final form at [http://dx.doi.org/10.1113/jphysiol.2013.259796]. In addition, authors may also transmit, print and share copies with colleagues, provided that there is no systematic distribution of the submitted version, e.g. posting on a listserve, network or automated delivery
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
Crystalline and magnetic structure of Ba2CuO3+{\delta} investigated by x-ray absorption spectroscopy and resonant inelastic x-ray scattering
Motivated by the recent synthesis of BaCuO (BCO), a high
temperature superconducting cuprate with putative ground state
symmetry, we investigated its electronic structure by means of Cu x-ray
absorption (XAS) and resonant inelastic x-ray scattering (RIXS) at the Cu
edge on a polycrystalline sample. We show that the XAS profile of BCO is
characterised by two peaks associated to inequivalent Cu sites, and that its
RIXS response features a single, sharp peak associated to crystal-field
excitations. We argue that these observations are only partially compatible
with the previously proposed crystal structure of BCO. Based on our
spectroscopic results and on previously published powder diffraction
measurements, we propose a crystalline structure characterized by two
inequivalent Cu sites located at alternated planes along the axis:
nominally trivalent Cu(1) belonging to very short Cu-O chains, and divalent
Cu(2) in the oxygen deficient CuO planes. We also analyze the
low-energy region of the RIXS spectra to estimate the magnitude of the magnetic
interactions in BCO and find that in-plane nearest neighbor superexchange
exceeds 120~meV, similarly to that of other layered cuprates. Although these
results do not support the pure ground state scenario, they hint
at a significant departure from the common quasi-2D electronic structure of
superconducting cuprates of pure symmetry
Multiple-magnon excitations shape the spin spectrum of cuprate parent compounds
Thanks to high resolution and polarization analysis, resonant inelastic x-ray
scattering (RIXS) magnetic spectra of La2CuO4, Sr2CuO2Cl2 and CaCuO2 reveal a
rich set of properties of the spin 1/2 antiferromagnetic square lattice of
cuprates. The leading single-magnon peak energy dispersion is in excellent
agreement with the corresponding inelastic neutron scattering measurements.
However, the RIXS data unveil an asymmetric lineshape possibly due to odd
higher order terms. Moreover, a sharp bimagnon feature emerges from the
continuum at (1/2,0), coincident in energy with the bimagnon peak detected in
optical spectroscopy. These findings show that the inherently complex spin
spectra of cuprates, an exquisite manifestation of quantum magnetism, can be
effectively explored by exploiting the richness of RIXS cross sections.Comment: 7 pages, 3 figure
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