133 research outputs found
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
Temperature dependence and resonance effects in Raman scattering of phonons in NdFeAsOF single crystals
We report plane-polarized Raman scattering spectra of iron oxypnictide
superconductor NdFeAsOF single crystals with varying fluorine
content. The spectra exhibit sharp and symmetrical phonon lines with a weak
dependence on fluorine doping . The temperature dependence does not show any
phonon anomaly at the superconducting transition. The Fe related phonon
intensity shows a strong resonant enhancement below 2 eV. We associate the
resonant enhancement to the presence of an interband transition around 2 eV
observed in optical conductivity. Our results point to a rather weak coupling
between Raman-active phonons and electronic excitations in iron oxypnictides
superconductors.Comment: 4 pages, 3 figures, to appear in Phys. Rev.
Electromagnon and phonon excitations in multiferroic TbMnO3
We have performed Raman measurements on TbMnO3 single crystal under magnetic
field along the three crystallographic directions. The flip of the spin spiral
plane creates an electromagnon excitation. In addition to the electromagnons
induced by the Heisenberg coupling, we have detected the electromagnon created
by the Dzyaloshinskii-Moriya interaction along the c axis. We have identified
all the vibrational modes of TbMnO3. Their temperature dependences show that
only one phonon observed along the polarization axis is sensitive to the
ferroelectric transition. This mode is tied to the Tb3+ ion displacements that
contribute to the ferroelectric polarization
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
Doping dependence of the lattice dynamics in Ba(FeCo)As studied by Raman spectroscopy
We report Raman scattering spectra of iron-pnictide superconductor
Ba(FeCo)As single crystals with varying cobalt content.
Upon cooling through the tetragonal-to-orthorhombic transition, we observe a
large splitting of the E in-plane phonon modes involving Fe and As
displacements. The splitting of the in-plane phonons at the transition is
strongly reduced upon doping and disappears for qualitatively
following the trend displayed by the Fe magnetic moment. The origin of the
splitting is discussed in terms of magnetic frustration inherent to
iron-pnictide systems and we argue that such enhanced splitting may be linked
to strong spin-phonon coupling.Comment: 6 pages, 6 figure
Amplitude `Higgs' mode in 2H-NbSe2 Superconductor
We report experimental evidences for the observation of the superconducting
amplitude mode, so-called `Higgs' mode in the charge density wave
superconductor 2H-NbSe2 using Raman scattering. By comparing 2H-NbSe2 and its
iso-structural partner 2H-NbS2 which shows superconductivity but lacks the
charge density wave order, we demonstrate that the superconducting mode in
2H-NbSe2 owes its spectral weight to the presence of the coexisting charge
density wave order. In addition, temperature dependent measurements in 2H-NbSe2
show a full spectral weight transfer from the charge density wave mode to the
superconducting mode upon entering the superconducting phase. Both observations
are fully consistent with a superconducting amplitude mode or Higgs mode.Comment: Accepted for publication in Phys. Rev. B Rapid Com. 5 pages with 3
figure
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