639 research outputs found
Cavity polariton optomechanics: Polariton path to fully resonant dispersive coupling in optomechanical resonators
Resonant photoelastic coupling in semiconductor nanostructures opens new
perspectives for strongly enhanced light-sound interaction in optomechanical
resonators. One potential problem, however, is the reduction of the cavity
Q-factor induced by dissipation when the resonance is approached. We show in
this letter that cavity-polariton mediation in the light-matter process
overcomes this limitation allowing for a strongly enhanced photon-phonon
coupling without significant lifetime reduction in the strongly-coupled regime.
Huge optomechanical coupling factors in the PetaHz/nm range are envisaged,
three orders of magnitude larger than the backaction produced by the mechanical
displacement of the cavity mirrors.Comment: 6 pages, 4 figure
Uncoupled excitons in semiconductor microcavities detected in resonant Raman scattering
We present an outgoing resonant Raman-scattering study of a GaAs/AlGaAs based microcavity embedded in a p-i-n junction. The p-i-n junction allows the vertical electric field to be varied, permitting control of exciton-photon detuning and quenching of photoluminescence which otherwise obscures the inelastic light scattering signals. Peaks corresponding to the upper and lower polariton branches are observed in the resonant Raman cross sections, along with a third peak at the energy of uncoupled excitons. This third peak, attributed to disorder activated Raman scattering, provides clear evidence for the existence of uncoupled exciton reservoir states in microcavities in the strong-coupling regime
Magnetotransport of lanthanum doped RuSr2GdCu2O8 - the role of gadolinium
Strongly underdoped RuSr_1.9La_0.1GdCu_2O_8 has been comprehensively studied
by dc magnetization, microwave measurements, magnetoresistivity and Hall
resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron
doping by La reduces the hole concentration in the CuO2 planes and completely
suppresses superconductivity. Microwave absorption, dc resistivity and ordinary
Hall effect data indicate that the carrier concentration is reduced and a
semiconductor-like temperature dependence is observed. Two magnetic ordering
transitions are observed. The ruthenium sublattice orders antiferromagnetically
at 155 K for low applied magnetic field and the gadolinium sublattice
antiferromagnetically orders at 2.8 K. The magnetoresistivity exhibits a
complicated temperature dependence due to the combination of the two magnetic
orderings and spin fluctuations. It is shown that the ruthenium magnetism
influences the conductivity in the RuO2 layers while the gadolinium magnetism
influences the conductivity in the CuO2 layers. The magnetoresistivity is
isotropic above 4 K, but it becomes anisotropic when gadolinium orders
antiferromagnetically.Comment: 7 pages, 9 figures, submitted to European Physical Journal
Coupling between Light and Terahertz-Frequency Acoustic Phonons in Ferroelectric BaTiO3 /SrTiO3 Superlattices
The acoustic phonons in epitaxial ferroelectric (BaTiO3 )n /(SrTiO3 )m superlattices (SLs) are investigated by high-resolution ultraviolet Raman scattering. The temperature dependence of the folded acoustic (FA) phonon Raman intensity through the ferroelectric transition is addressed. A comparison of this behavior between SLs with different number of ferroelectric BaTiO3 unit cells n and spacer SrTiO3 unit cells m is presented. A mechanism involving the strain modulation of the spatially varying ferroelectric polarization is introduced to explain the temperature dependence of the FA phonon scattering. The temperature dependence of the polarization can be derived from an analysis of the first-order optical phononspectra. Using this information, the observed temperature dependence of the whole set of SLs with different n can be consistently accounted for with the presented model. Atomistic shell-model simulations of the spatial pattern of the SL polarization are presented to explain the variation of the FA-spectral intensity for SLs with different m and the experimental fact that no high-order FA-replicas are observed. These results demonstrate the strong coupling between THz hypersound, charge, and light in these multifunctional nanoscale ferroelectrics.Fil: Bruchhausen, Axel Emerico. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentina. University of Konstanz; AlemaniaFil: Fainstein, Alejandro. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; ArgentinaFil: Tinte, Silvia Noemi. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Santa Fe. Instituto de Desarrollo Tecnológico para la Industria Química (i); ArgentinaFil: Soukiassian, A.. University Park; Estados UnidosFil: Schlom, D. G.. Cornell University; Estados UnidosFil: Xi, X. X.. Cornell University; Estados Unidos. Comisión Nacional de Energía Atómica. Gerencia del Area de Energía Nuclear. Instituto Balseiro; Argentina. Comisión Nacional de Energía Atómica. Gerencia del Area de Investigaciones y Aplicaciones No Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentin
Efecto de una corriente continua en los espectros Raman de dos magnones en Bi₂Sr₂Ca₁ Cu₂O₈₊∗
Es conocido que los óxidos superconductores de alta temperatura tienen como característica principal el orden antiferromagnético de los planos de CuO₂. Esto permite detectar, con técnicas comunes a espectroscopia Raman, scattering inelástico de pares de magnones como una banda ancha centrada alrededor de 2500 cm-¹.
En esta comunicación presentamos medidas preliminares de dichas excitaciones en pastillas super-conductoras de Bi-2212 nominalmente puras y semiconductoras dopada con Fe bajo una corriente DC a temperaturas inferiores a Tc. Encontramos que bajo estas condiciones aumenta el ancho medio a media altura del perfil aproximadamente simétrico de la banda de dos magnones de la pastilla pura y que del lado de más altas frecuencias hay un significativo incremento en su intensidad. Estas medidas sugieren una explicación según la cual los portadores involucrados en la corriente continua afectarían la interacción de intercambio a través de una interacción electrón magnón.Facultad de Ciencias Exacta
Microcavity exciton-polariton mediated Raman scattering: Experiments and theory
We studied the intensity of resonant Raman scattering due to optical phonons
in a planar II-VI-type semiconductor microcavity in the regime of strong
coupling between light and matter. Two different sets of independent
experiments were performed at near outgoing resonance with the middle polariton
(MP)branch of the cavity. In the first, the Stokes-shifted photons were kept at
exact resonance with the MP, varying the photonic or excitonic character of the
polariton. In the second, only the incoming light wavelength was varied, and
the resonant profile of the inelastic scattered intensity was studied when the
system was tuned out of the resonant condition. Taking some matrix elements as
free parameters, both independent experiments are quantitatively described by a
model which incorporates lifetime effects in both excitons and photons, and the
coupling of the cavity photons to the electron-hole continuum. The model is
solved using a Green's function approach which treats the exciton-photon
coupling nonperturbatively.Comment: 10 pages, 6 figure
A Transport and Microwave Study of Superconducting and Magnetic RuSr2EuCu2O8
We have performed susceptibility, thermopower, dc resistance and microwave
measurements on RuSr2EuCu2O8. This compound has recently been shown to display
the coexistence of both superconducting and magnetic order. We find clear
evidence of changes in the dc and microwave resistance near the magnetic
ordering temperature (132 K). The intergranular effects were separated from the
intragranular effects by performing microwave measurements on a sintered
ceramic sample as well as on a powder sample dispersed in an epoxy resin. We
show that the data can be interpreted in terms of the normal-state resistivity
being dominated by the CuO2 layers with exchange coupling to the Ru moments in
the RuO2 layers. Furthermore, most of the normal-state semiconductor-like
upturn in the microwave resistance is found to arise from intergranular
transport. The data in the superconducting state can be consistently
interpreted in terms of intergranular weak-links and an intragranular
spontaneous vortex phase due to the ferromagnetic component of the
magnetization arising from the RuO2 planes.Comment: 20 pages including 6 figures in pdf format. To be published in Phys.
Rev.
Structural analysis, magnetic and transport properties of the (Ru1-xCox)Sr2GdCu2O8 system
The effects of Co substitution on structural and superconducting properties
of RuSr2GdCu2O8 compound have been studied. Rietveld refinements of the X-ray
diffraction patterns indicate that the cobalt ion progressively replaces
ruthenium sites. This replacement induces significant changes on the crystal
structure and on the magnetic and superconducting properties. The effects Co
substitution on the superconducting behaviour, and more particulary on the
changes induce by the hole doping mechanism, were investigated in
(Ru1-xCox)Sr2GdCu2O8 by a "bond valence sum" analysis with Co content from x=
0.0 to x = 0.2. The weak ferromagnetic transition at Tm= 138.2 K is shifted to
lower temperature, and suppressed at higher Co content. From the
crystallographic point of view the Ru-O(1)-Cu bond angle, associated to the
rotation of the RuO6 octahedra, around the c-axis remain essetially constant
when Ru is substituted by Co. Furthermore, increasing Co content has the effect
to increase the weak ferromagnetic moment, which may be interpreted as the main
responsible for breaking the delicate balance between magnetic and
superconducting ordering.Comment: 21 pages, 8 figure
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