230 research outputs found
Signatures of nematic quantum critical fluctuations in the Raman spectra of lightly doped cuprates
We consider the lightly doped cuprates YCaBaCuO
and LaSrCuO (with ,0.04), where the presence of a
fluctuating nematic state has often been proposed as a precursor of the stripe
(or, more generically, charge-density wave) phase, which sets in at higher
doping. We phenomenologically assume a quantum critical character for the
longitudinal and transverse nematic, and for the charge-ordering fluctuations,
and investigate the effects of these fluctuations in Raman spectra. We find
that the longitudinal nematic fluctuations peaked at zero transferred momentum
account well for the anomalous Raman absorption observed in these systems in
the channel, while the absence of such effect in the channel
may be due to the overall suppression of Raman response at low frequencies,
associated with the pseudogap. While in YCaBaCuO the
low-frequency lineshape is fully accounted by longitudinal nematic collective
modes alone, in LaSrCuO also charge-ordering modes with finite
characteristic wavevector are needed to reproduce the shoulders observed in the
Raman response. This different involvement of the nearly critical modes in the
two materials suggests a different evolution of the nematic state at very low
doping into the nearly charge-ordered state at higher doping.Comment: 12 pages with 10 figures, to appear in Phys. Rev. B 201
Electron interactions and charge ordering in LaSrCuO
We present results of inelastic light scattering experiments on
single-crystalline LaSrCuO in the doping range and TlBaCuO at and . The main
emphasis is placed on the response of electronic excitations in the
antiferromagnetic phase, in the pseudogap range, in the superconducting state,
and in the essentially normal metallic state at , where no
superconductivity could be observed. In most of the cases we compare B
and B spectra which project out electronic properties close to
and , respectively. In the channel of electron-hole excitations
we find universal behavior in B symmetry as long as the material
exhibits superconductivity at low temperature. In contrast, there is a strong
doping dependence in B symmetry: (i) In the doping range we observe rapid changes of shape and temperature dependence of the
spectra. (ii) In LaSrCuO new structures appear for
which are superposed on the electron-hole continuum. The temperature dependence
as well as model calculations support an interpretation in terms of
charge-ordering fluctuations. For the response from fluctuations
disappears at B and appears at B symmetry in full agreement with
the orientation change of stripes found by neutron scattering. While, with a
grain of salt, the particle-hole continuum is universal for all cuprates the
response from fluctuating charge order in the range is so
far found only in LaSrCuO. We conclude that
LaSrCuO is close to static charge order and, for this reason,
may have a suppressed .Comment: 17 pages, 15 figure
Bosons in high temperature superconductors: an experimental survey
We review a number of experimental techniques that are beginning to reveal
fine details of the bosonic spectrum \alpha^2F(\Omega) that dominates the
interaction between the quasiparticles in high temperature superconductors.
Angle-resolved photo emission (ARPES) shows kinks in electronic dispersion
curves at characteristic energies that agree with similar structures in the
optical conductivity and tunnelling spectra. Each technique has its advantages.
ARPES is momentum resolved and offers independent measurements of the real and
imaginary part of the contribution of the bosons to the self energy of the
quasiparticles. The optical conductivity can be used on a larger variety of
materials and with the use of maximum entropy techniques reveals rich details
of the spectra including their evolution with temperature and doping. Scanning
tunnelling spectroscopy offers spacial resolution on the unit cell level. We
find that together the various spectroscopies, including recent Raman results,
are pointing to a unified picture of a broad spectrum of bosonic excitations at
high temperature which evolves, as the temperature is lowered into a peak in
the 30 to 60 meV region and a featureless high frequency background in most of
the materials studied. This behaviour is consistent with the spectrum of spin
fluctuations as measured by magnetic neutron scattering. However, there is
evidence for a phonon contribution to the bosonic spectrum as well.Comment: 71 pages, 52 figure
Quantitative comparison of single- and two-particle properties in the cuprates
We explore the strong variations of the electronic properties of
copper-oxygen compounds across the doping phase diagram in a quantitative way.
To this end we calculate the electronic Raman response on the basis of results
from angle-resolved photoemission spectroscopy (ARPES). In the limits of our
approximations we find agreement on the overdoped side and pronounced
discrepancies at lower doping. In contrast to the successful approach for the
transport properties at low energies, the Raman and the ARPES data cannot be
reconciled by adding angle-dependent momentum scattering. We discuss possible
routes towards an explanation of the suppression of spectral weight close to
the points which sets in abruptly close to 21% doping.Comment: 7 pages, 4 figure
Multi-gap superconductivity in a BaFe1.84Co0.16As2 film from optical measurements at terahertz frequencies
We measured the THz reflectance properties of a high quality epitaxial thin
film of the Fe-based superconductor BaFeCoAs with
T=22.5 K. The film was grown by pulsed laser deposition on a DyScO
substrate with an epitaxial SrTiO intermediate layer. The measured
spectrum, i.e. the reflectivity ratio between the superconducting and
normal state reflectance, provides clear evidence of a superconducting gap
close to 15 cm. A detailed data analysis shows that a
two-band, two-gap model is absolutely necessary to obtain a good description of
the measured spectrum. The low-energy gap results to be
well determined (=15.50.5 cm), while the value of the
high-energy gap is more uncertain (=557 cm).
Our results provide evidence of a nodeless isotropic double-gap scenario, with
the presence of two optical gaps corresponding to 2 values close
to 2 and 7.Comment: Published Versio
Anisotropic Structure of the Order Parameter in FeSe0.45Te0.55 Revealed by Angle Resolved Specific Heat
The symmetry and structure of the superconducting gap in the Fe-based
superconductors are the central issue for understanding these novel materials.
So far the experimental data and theoretical models have been highly
controversial. Some experiments favor two or more constant or nearly-constant
gaps, others indicate strong anisotropy and yet others suggest gap zeros
("nodes"). Theoretical models also vary, suggesting that the absence or
presence of the nodes depends quantitatively on the model parameters. An
opinion that has gained substantial currency is that the gap structure, unlike
all other known superconductors, including cuprates, may be different in
different compounds within the same family. A unique method for addressing this
issue, one of the very few methods that are bulk and angle-resolved, calls for
measuring the electronic specific heat in a rotating magnetic field, as a
function of field orientation with respect to the crystallographic axes. In
this Communication we present the first such measurement for an Fe-based
high-Tc superconductor (FeBSC). We observed a fourfold oscillation of the
specific heat as a function of the in-plane magnetic field direction, which
allowed us to identify the locations of the gap minima (or nodes) on the Fermi
surface. Our results are consistent with the expectations of an extended s-wave
model with a significant gap anisotropy on the electron pockets and the gap
minima along the \Gamma M (or Fe-Fe bond) direction.Comment: 32 pages, 7 figure
Instrumented fusion of thoracolumbar fracture with type I mineralized collagen matrix combined with autogenous bone marrow as a bone graft substitute: a four-case report
In order to avoid the morbidity from autogenous bone harvesting, bone graft substitutes are being used more frequently in spinal surgery. There is indirect radiological evidence that bone graft substitutes are efficacious in humans. The purpose of this four-case study was to visually, manually, and histologically assess the quality of a fusion mass produced by a collagen hydroxyapatite scaffold impregnated with autologous bone marrow aspirate for posterolateral fusion. Four patients sustained an acute thoracolumbar fracture and were treated by short posterior segment fusion using the AO fixateur interne. Autologous bone marrow (iliac crest) impregnated hydroxyapatite-collagen scaffold was laid on the decorticated posterior elements. Routine implant removal was performed after a mean of 15.3 months (12–20). During this second surgery, fusion mass was assessed visually and manually. A bone biopsy was sent for histological analysis of all four cases. Fusion was confirmed in all four patients intraoperatively and sagittal stress testing confirmed mechanical adequacy of the fusion mass. Three out of the four (cases 2–4) had their implants removed between 12 and 15 months after the index surgery. All their histological cuts showed evidence of newly formed bone and presence of active membranous and/or enchondral ossification foci. The last patient (case 1) underwent implant removal at 20 months and his histological cuts showed mature bone, but no active ossification foci. This four-case report suggests that the fusion mass produced by a mineralized collagen matrix graft soaked in aspirated bone marrow is histologically and mechanically adequate in a thoracolumbar fracture model. A larger patient series and/or randomized controlled studies are warranted to confirm these initial results
Treatment of osteonecrosis of the femoral head using autologous cultured osteoblasts: a case report
<p>Abstract</p> <p>Introduction</p> <p>Osteonecrosis of the femoral head is a progressive disease that leads to femoral head collapse and osteoarthritis. Our goal in treating osteonecrosis is to preserve, not to replace, the femoral head.</p> <p>Case presentation</p> <p>We present the case of a patient with bilateral osteonecrosis of the femoral head treated with autologous cultured osteoblast injection.</p> <p>Conclusion</p> <p>Although our experience is limited to one patient, autologous cultured osteoblast transplantation appears to be effective for treating the osteonecrosis of femoral head.</p
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