720 research outputs found
Role of Symmetry in Raman Spectroscopy of Unconventional Superconductors
The role of symmetry of the inelastic light scattering amplitude, the
superconducting energy gap, and the underlying Fermi surface manifold on the
Raman spectra of unconventional superconductors is discussed in detail.
Particular emphasis is placed on both single and bi-layer superconductors. It
is found that the channel may be the most sensitive to doping due to
the role of the Van Hove singularity. Lastly the effects of both disorder and
spin fluctuations are considered. The theory imposes strong constraints on both
the magnitude and symmetry of the energy gap for the bi-layer cuprates,
indicating that a nearly identical energy gap of symmetry
provides a best fit to the data.Comment: 12 pages, 4 postscript files, 1 tabl
Symmetry dependence of phonon lineshapes in superconductors with anisotropic gaps
The temperature dependence below of the lineshape of optical phonons
of different symmetry as seen in Raman scattering is investigated for
superconductors with anisotropic energy gaps. It is shown that the symmetry of
the electron-phonon vertex produces non-trivial couplings to an anisotropic
energy gap which leads to unique changes in the phonon lineshape for phonons of
different symmetry. The phonon lineshape is calculated in detail for
and phonons in a superconductor with pairing
symmetry. The role of satellite peaks generated by the electron-phonon coupling
are also addressed. The theory accounts for the substantial phonon narrowing of
the phonon, while narrowing of the phonon which is
indistinguishable from the normal state is shown, in agreement with recent
measurements on BSCCO.Comment: 15 pages (3 Figures available upon request), Revtex, 1
Raman Scattering in Cuprate Superconductors
A theory for electronic Raman scattering in the cuprate superconductors is
presented with a specific emphasis on the polarization dependence of the
spectra which can infer the symmetry of the energy gap. Signatures of the
effects of disorder on the low frequency and low temperature behavior of the
Raman spectra for different symmetry channels provide detailed information
about the magnitude and the phase of the energy gap. Properties of the theory
for finite T are discussed and compared to recent data concerning the doping
dependence of the Raman spectra in cuprate superconductors, and remaining
questions are addressed.Comment: 27 pages, 11 figures, style file include
Electronic Raman response in anisotropic metals
Using a generalized response theory we derive the electronic Raman response
function for metals with anisotropic relaxation rates. The calculations account
for the long--range Coulomb interaction and treat the collision operator within
a charge conserving relaxation time approximation. We extend earlier treatments
to finite wavenumbers () and incorporate inelastic
electron--electron scattering besides elastic impurity scattering. Moreover we
generalize the Lindhard density response function to the Raman case. Numerical
results for the quasiparticle scattering rate and the Raman response function
for cuprate superconductors are presented.Comment: 5 pages, 4figures. accepted in PRB (Brief Report), in pres
Universal zero-frequency Raman slope in a d-wave superconductor
It is known that for an unconventional superconductor with nodes in the gap,
the in-plane microwave or dc conductivity saturates at low temperatures to a
universal value independent of the impurity concentration. We demonstrate that
a similar feature can be accessed using channel-dependent Raman scattering. It
is found that, for a -wave superconductor, the slope of
low-temperature Raman intensity at zero frequency is universal in the
and channels, but not in the channel. Moreover, as opposed to
the microwave conductivity, universal Raman slopes are sensitive not only to
the existence of a node, but also to different pairing states and should allow
one to distinguish between such pairing states.Comment: 5 page
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
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