165 research outputs found
Electronic Raman scattering on under-doped Hg-1223 high-Tc superconductors:investigations on the symmetry of the order parameter
In order to obtain high quality, reliable electronic Raman spectra of a
high-Tc superconductor compound, we have studied strongly under-doped
HgBa2Ca2Cu3O8+d. This choice was made such as to i)minimize oxygen disorder in
the Hg-plane generated by oxygen doping ii) avoid the need of phonon background
subtraction from the raw data iii)eliminate traces of parasitic phases
identified and monitored on the crystal surface. Under these experimental
conditions we are able to present the pure electronic Raman response function
in the B2g, B1g, A1g+B2g and A1g+B1g channels. The B2g spectrum exhibits a
linear frequency dependence at low energy whereas the B1g one shows a
cubic-like dependence. The B2g and B1g spectra display two well defined maxima
at 5.6kBTc and 9kBTc respectively. In mixed A1g channels an intense electronic
peak centered around 6.4 kBTc is observed. The low energy parts of the spectra
correspond to the electronic response expected for a pure dx2-y2 gap symmetry
and can be fitted up to the gap energy for the B1g channel. However, in the
upper parts, the relative position of the B1g and B2g peaks needs expanding the
B2g Raman vertex to second order Fermi surface harmonics to fit the data with
the dx2-y2 model. The sharper and more intense A1g peak appears to challenge
the Coulomb screening efficiency present for this channel. As compared to
previous data on more optimally doped, less stoichiometric
Hg-1223 compounds, this work reconciles the electronic Raman spectra of
under- doped Hg-1223 crystals with the dx2-y2 model, provided that the oxygen
doping is not too strong. This apparent extreme sensitivity of the electronic
Raman spectra to the low lying excitations induced by oxygen doping in the
superconducting state is emphasized here and remains an open question.Comment: 12 pages, 5 figure
Resonant Raman scattering in mercurate single crystals
We report resonant electronic Raman scattering in optimally doped single
layer HgBaCuO (Hg-1201) and trilayer
HgBaCaCuO (Hg-1223) single crystals. Analysis of the
and B channels in the superconducting state of Hg-1201
advocates for a gap having d-wave symmetry. In addition a resonant study
pair-breaking peak and the peak suggests that the
peak is not directly related to the d-wave superconducting gap amplitude.
Comparison with trilayer Hg-1223 demonstrates the universal behavior of this
two energy scales in optimally doped cuprates.Comment: 4 pages, 4 figures, M2S-Rio (invited paper). to appear in Physica
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
Evidence for two distinct energy scales in the Raman spectra of YBa2(CuNi)O6.95
We report low energy electronic Raman scattering from Ni-substituted
YBa2Cu3O6.95 single crystals with Tc ranging from 92.5 K to 78 K. The fully
symmetrical A1g channel and the B1g channel which is sensitive to the dx2-y2
gap maximum have been explored. The energy of the B1g pair-breaking peak
remains constant under Ni doping while the energy of the A1g peak scales with
Tc (EA1g/Tc=5). Our data show that the A1g peak tracks the magnetic resonance
peak observed in inelastic neutron scattering yielding a key explanation to the
long-standing problem of the origin the A1g peak.Comment: 10 pages, 4 figures and 1 tabl
Magnetic transitions in CaMn7O12 : a Raman observation of spin-phonon couplings
The quadruple Calcium manganite (CaMn7O12) is a multiferroic material that
exhibits a giant magnetically-induced ferroelectric polarization which makes it
very interesting for magnetoelectric applications. Here, we report the Raman
spectroscopy study on this compound of both the phonon modes and the low energy
excitations from 4 K to room temperature. A detailed study of the Raman active
phonon excitations shows that three phonon modes evidence a spin-phonon
coupling at TN2 = 50 K. In particular, we show that the mode at 432 cm-1
associated to Mn(B)O6 (B position of the perovskite) rotations around the [111]
cubic diagonal is impacted by the magnetic transition at 50 K and its coupling
to the new modulation of the Mn spin in the (a,b) plane. At low energies, two
large low energy excitations are observed at 25 and 47 cm-1. The first one
disappears at 50 K and the second one at 90 K. We have associated these
excitations to electro-magneto-active modes
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
Impact of the Spin Density Wave Order on the Superconducting Gap of Ba(FeCo)As
We report a doping dependent electronic Raman scattering measurements on
iron-pnictide superconductor Ba(FeCo)As single crystals. A
strongly anisotropic gap is found at optimal doping for x=0.065 with
. Upon entering the coexistence region between
superconducting (SC) and spin-density-wave (SDW) orders, the effective pairing
energy scale is strongly reduced. Our results are interpreted in terms of a
competition between SC and SDW orders for electronic state at the Fermi level.
Our findings advocate for a strong connection between the SC and SDW gaps
anisotropies which are both linked to interband interactions.Comment: 4 pages, 3 figure
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