242 research outputs found
Superconductivity-induced Phonon Renormalization on NaFeCoAs
We report a study of the lattice dynamics in superconducting NaFeAs (Tc = 8
K) and doped NaFe0.97Co0.03As (Tc = 20 K) using Raman light scattering. Five of
the six phonon modes expected from group theory are observed. In contrast with
results obtained on iso-structural and iso-electronic LiFeAs, anomalous
broadening of Eg(As) and A1g(Na) modes upon cooling is observed in both
samples. In addition, in the Co-doped sample, a superconductivity-induced
renormalization of the frequency and linewidth of the B1g(Fe) vibration is
observed. This renormalization can not be understood within a single band and
simple multi-band approaches. A theoretical model that includes the effects of
SDW correlations along with sign-changing s-wave pairing state and interband
scattering has been developed to explain the observed behavior of the B1g(Fe)
mode.Comment: 10 pages; 6 figure
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
Comparison of charge modulations in LaBaCuO and YBaCuO
A charge modulation has recently been reported in (Y,Nd)BaCuO
[Ghiringhelli {\em et al.} Science 337, 821 (2013)]. Here we report Cu
edge soft x-ray scattering studies comparing the lattice modulation associated
with the charge modulation in YBaCuO with that associated with
the well known charge and spin stripe order in LaBaCuO.
We find that the correlation length in the CuO plane is isotropic in both
cases, and is \AA for LaBaCuO and \AA for YBaCuO. Assuming weak inter-planar correlations of
the charge ordering in both compounds, we conclude that the order parameters of
the lattice modulations in LaBaCuO and
YBaCuO are of the same order of magnitude.Comment: 3 pages, 2 figure
Raman Scattering Study of the Lattice Dynamics of Superconducting LiFeAs
We report an investigation of the lattice dynamical properties of LiFeAs
using inelastic light scattering. Five out of the six expected phonon modes are
observed. The temperature evolution of their frequencies and linewidths is in
good agreement with an anharmonic-decay model. We find no evidence for
substantial electron-phonon coupling, and no superconductivity-induced phonon
anomalies.Comment: 5 pages, 3 figures, 1 tabl
Momentum-dependent charge correlations in YBaCuO superconductors probed by resonant x-ray scattering: Evidence for three competing phases
We have used resonant x-ray scattering to determine the momentum dependent
charge correlations in YBaCuO samples with highly ordered
chain arrays of oxygen acceptors (ortho-II structure). The results reveal
nearly critical, biaxial charge density wave (CDW) correlations at in-plane
wave vectors (0.315, 0) and (0, 0.325). The corresponding scattering intensity
exhibits a strong uniaxial anisotropy. The CDW amplitude and correlation length
are enhanced as superconductivity is weakened by an external magnetic field.
Analogous experiments were carried out on a YBaCuO crystal with
a dilute concentration of spinless (Zn) impurities, which had earlier been
shown to nucleate incommensurate magnetic order. Compared to pristine crystals
with the same doping level, the CDW amplitude and correlation length were found
to be strongly reduced. These results indicate a three-phase competition
between spin-modulated, charge-modulated, and superconducting states in
underdoped YBaCuO.Comment: 6 pages, 3 figures revised version, to appear in Phys. Rev. Let
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