639 research outputs found
Evolution of the gaps through the cuprate phase-diagram
The actual physical origin of the gap at the antinodes, and a clear
identification of the superconducting gap are fundamental open issues in the
physics of high- superconductors. Here, we present a systematic electronic
Raman scattering study of a mercury-based single layer cuprate, as a function
of both doping level and temperature. On the deeply overdoped side, we show
that the antinodal gap is a true superconducting gap. In contrast, on the
underdoped side, our results reveal the existence of a break point close to
optimal doping below which the antinodal gap is gradually disconnected from
superconductivity. The nature of both the superconducting and normal state is
distinctly different on each side of this breakpoint
Coupling between quasiparticles and a bosonic mode in the normal state of HgBaCuO
We report a doping dependent study of the quasiparticles dynamics in
HgBaCuO via Electronic Raman Scattering. A well-defined energy
scale is found in the normal state dynamics of the quasiparticles over a broad
doping range. It is interpreted as evidence for coupling between the
quasiparticles and a collective bosonic mode whose energy scale depend only
weakly with doping. We contrast this behavior with that of the superconducting
gap whose amplitude near the node continuously decreases towards the underdoped
regime. We discuss the implications of our findings on the nature of the
collective mode and argue that electron-phonon coupling is the most natural
explanation.Comment: 5 pages, 4 figure
The nodal gap component as a good candidate for the superconducting order parameter in cuprates
Although more than twenty years have passed since the discovery of high
temperature cuprate superconductivity, the identification of the
superconducting order parameter is still under debate. Here, we show that the
nodal gap component is the best candidate for the superconducting order
parameter. It scales with the critical temperature over a wide doping
range and displays a significant temperature dependence below in both the
underdoped and the overdoped regimes of the phase diagram. In contrast, the
antinodal gap component does not scale with in the underdoped side and
appears to be controlled by the pseudogap amplitude. Our experiments establish
the existence of two distinct gaps in the underdoped cuprates
Inelastic X-ray scattering studies of phonon dispersions in superconductors at high pressures
Electron-phonon interaction is of central importance for the electrical and
heat transport properties of metals, and is directly responsible for
charge-density-waves or (conventional) superconducting instabilities. The
direct observation of phonon dispersion anomalies across electronic phase
transitions can provide insightful information regarding the mechanisms
underlying their formation. Here, we review the current status of phonon
dispersion studies in superconductors under hydrostatic and uniaxial pressure.
Advances in the instrumentation of high resolution inelastic X-ray scattering
beamlines and pressure generating devices allow these measurements to be
performed routinely at synchrotron beamlines worldwide.Comment: 8 pages, 6 figures. Invited review submitted to Superconductor
Science and Technology, Focus issue on Hydride & High-Pressure
Superconductors. References in figure caption fixed. Hyperlinks adde
Two Distinct Electronic Contributions in the Fully Symmetric Raman Response of High Cuprates
We show by non resonant effect in HgBaCuO (Hg-1201)and by Zn
substitutions in YBaCuO (Y-123) compounds that the fully
symmetric Raman spectrum has two distinct electronic contributions. The
A response consists in the superconducting pair breaking peak at the
2 energy and a collective mode close to the magnetic resonance energy.
These experimental results reconcile the \textit{d-wave} model to the A
Raman response function in so far as a collective mode that is distinct from
the pair breaking peak is present in the A channel.Comment: 4 pages, 2 figure
Inelastic x-ray scattering investigations of lattice dynamics in SmFeAsOF superconductors
We report measurements of the phonon density of states as measured with
inelastic x-ray scattering in SmFeAsOF powders. An unexpected
strong renormalization of phonon branches around 23 meV is observed as fluorine
is substituted for oxygen. Phonon dispersion measurements on
SmFeAsOF single crystals allow us to identify the 21 meV A
in-phase (Sm,As) and the 26 meV B (Fe,O) modes to be responsible for
this renormalization, and may reveal unusual electron-phonon coupling through
the spin channel in iron-based superconductors.Comment: 4 pages, 3 figures, submitted for SNS2010 conference proceeding
Coherent quasi-particles-to-incoherent hole-carriers crossover in underdoped cuprates
In underdoped cuprates, only a portion of the Fermi surface survives as Fermi
arcs due to pseudogap opening. In hole-doped LaCuO, we have deduced
the "coherence temperature" of quasi-particles on the Fermi arc above
which the broadened leading edge position in angle-integrated photoemission
spectra is shifted away from the Fermi level and the quasi-particle concept
starts to lose its meaning. is found to rapidly increase with hole
doping, an opposite behavior to the pseudogap temperature . The
superconducting dome is thus located below both and , indicating
that the superconductivity emerges out of the coherent Fermionic
quasi-particles on the Fermi arc. remains small in the underdoped
region, indicating that incoherent charge carriers originating from the Fermi
arc are responsible for the apparently metallic transport at high temperatures
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