Search results for "Phonon"
showing 10 items of 466 documents
Probing Nanoscale Ferroelectricity by Ultraviolet Raman Spectroscopy
2006
We demonstrated that ultraviolet Raman spectroscopy is an effective technique to measure the transition temperature ( T c ) in ferroelectric ultrathin films and superlattices. We showed that one-unit-cell-thick BaTiO 3 layers in BaTiO 3 /SrTiO 3 superlattices are not only ferroelectric (with T c as high as 250 kelvin) but also polarize the quantum paraelectric SrTiO 3 layers adjacent to them. T c was tuned by ∼500 kelvin by varying the thicknesses of the BaTiO 3 and SrTiO 3 layers, revealing the essential roles of electrical and mechanical boundary conditions for nanoscale ferroelectricity.
Low-temperature exciton absorption in InSe under pressure.
1992
We have investigated the effect of pressure on the lowest direct band-edge exciton of the layered semiconductor InSe by optical-absorption measurements at 10 K and for pressures up to 4 GPa. The Elliott-Toyozawa formalism is used to analyze the line shape of the exciton absorption spectra. In this way we determine the pressure dependence of the lowest direct band gap, the exciton binding energy, and the exciton linewidth. The band gap exhibits a pronounced nonlinear shift with pressure, which is a consequence of the strong anisotropy of intralayer and interlayer bonding. The exciton binding energy decreases with pressure, mainly due to the large increase of the low-frequency dielectric cons…
Direction-dependent elastic properties and phononic behavior of PMMA/BaTiO 3 nanocomposite thin films
2017
Determination of the anisotropic mechanical properties of nanostructured hybrid films is of great importance to improve fabrication and to enable reliable utility. Here, we employ spontaneous Brillouin light spectroscopy to record the phononic dispersion relation along the two symmetry directions in a supported PMMA (poly(methylmethacrylate))-BaTiO3 hybrid superlattice (SL) with a lattice constant of about 140 nm. Several dispersive elastic modes are resolved for in-plane wave propagation, whereas along the periodicity direction the SL opens a wide propagation stop band for hypersonic phonons and near UV photons both centered at about 280 nm. A thorough theoretical analysis based on the fin…
Transition probabilities in 31P and 31S : A test for isospin symmetry
2021
International audience; Excited states in the mirror nuclei 31P and 31S were populated in the 1p and 1n exit channels of the reaction 20Ne + 12C, at a beam energy of 33 MeV. The 20Ne beam was delivered for the first time by the Piave-Alpi accelerator of the Laboratori Nazionali di Legnaro. Angular correlations of coincident γ-rays and Doppler-shift attenuation lifetime measurements were performed using the multi-detector array GASP in conjunction with the EUCLIDES charged particle detector. In the observed B(E1) strengths, the isoscalar component, amounting to 24% of the isovector one, provides strong evidence for breaking of the isospin symmetry in the A=31 mass region. Self-consistent bey…
Evidence of octupole-phonons at high spin in 207Pb
2019
A lifetime measurement of the 19/2 state in Pb has been performed using the Recoil Distance Doppler-Shift (RDDS) method. The nuclei of interest were produced in multi-nucleon transfer reactions induced by a Pb beam impinging on a Mo enriched target. The beam-like nuclei were detected and identified in terms of their atomic mass number in the VAMOS++ spectrometer while the prompt γ rays were detected by the AGATA tracking array. The measured large reduced transition probability B(E3,19/2→13/2)=40(8) W.u. is the first indication of the octupole phonon at high spin in Pb. An analysis in terms of a particle-octupole-vibration coupling model indicates that the measured B(E3) value in Pb is compa…
X-ray thermal-diffuse-scattering study of soft modes in paraelectricBaTiO3
1995
Anomalous x-ray thermal diffuse scattering (TDS) from the paraelectric ${\mathrm{BaTiO}}_{3}$ has been measured as a function of temperature using synchrotron radiation. Sheets of intensities that were previously reported have been confirmed. The origin of the observed TDS intensities is attributed to the soft on-(100) TA modes and overdamped [010${]}_{\mathrm{TO}}$ mode for reduced wave vector qg0.25 and 0.25, respectively. In agreement with the previous neutron inelastic scattering experiment, our results support the notion of the one-dimensionally correlated optic motion of atoms.
Excitation and decay of two-phonon giant dipole resonances
1999
Abstract In heavy ion collisions at near relativistic energies, electromagnetic excitation of the double giant dipole resonance occurs with large cross sections. We summarize the presently available experimental data and discuss related theoretical efforts. Emphasis is paid to the question of anharmonicities and to the damping of the two-phonon states.
Proton-Deuteron Elastic Scattering for E > 0
1999
We report on the first reliable numerical results for proton-deuteron elastic scattering observables for energies above the deuteron breakup thresh- old, for the Paris potential. The calculations have been performed within the screening and renormalisation approach. The theoretical results are compared with recent experimental data.
Spectroscopy of Rn, Ra and Th isotopes using multi-nucleon transfer reactions
1999
Abstract High-spin spectroscopy of Rn, Ra and Th isotopes has been performed. The nuclei have been populated using multi-nucleon transfer reactions involving a 232 Th target and a 136 Xe projectile. This type of reaction offers the only mechanism for populating high-spin states in many of these nuclei. Interleaving bands with opposite parities have been observed to high spin ( ∼28 h ) in 218,220,222 Rn, 222,224,226,228 Ra and 228,230,234 Th. A systematic study of the rotational alignment properties of octupole bands in radon, radium and thorium isotopes reveals information concerning the role of the octupole phonon and the onset of stable octupole deformation with increasing rotational freq…
Two-phonon octupole excitation inGd146
2010
Based on experimental evidence from the $^{144}\mathrm{Sm}$($\ensuremath{\alpha},2n$) reaction, the $3484.7$-keV ${6}^{+}$ state in $^{146}\mathrm{Gd}$ is identified as the highest-spin member of the ${3}^{\ensuremath{-}}\ensuremath{\bigotimes}{3}^{\ensuremath{-}}$ two-phonon octupole quartet. A previously unknown $\ensuremath{\gamma}$ line of $1905.8$ keV and $E3$ character feeding the ${3}^{\ensuremath{-}}$ octupole state has been observed. These results represent the first observation of a ${6}^{+}\ensuremath{\rightarrow}{3}^{\ensuremath{-}}\ensuremath{\rightarrow}{0}^{+}$ cascade of two $E3$ transitions in an even-even nucleus and provide strong support for the interpretation of the ${6…