Anharmonic scattering processes and relaxation of quasi-transverse modes in cubic crystals with positive or negative anisotropy of second-order elastic moduli

Quasi-transverse ultrasound absorption due to point defects and anharmonic scattering processes in cubic crystals with positive and negative anisotropies of the second-order elastic moduli

“…In other words, will the ultrasound absorption anisotropy be determined predominantly by the anisotropy of the harmonic or the anharmonic energy? Such analysis was performed [21] for the relaxation rates of quasi-transverse phonons in terms of the Landau-Rumer mechanism. Unlike earlier calculations, the analysis took into account exactly the effect of the cubic anisotropy on both the spectrum of the vibrational branches involved in the energy conservation law and the phonon polarization vectors.…”

“…Thus, we take into account explicitly the phonon polarization vectors for quasi-transverse phonons, but use the approximation of pure modes for quasi-longitudinal vibrations. Therefore, our calculations of the ultrasound absorption in an arbitrary direction of the wavevector will allow for the contribution of the longitudinal component to the transverse-longitudinal vibrations similarly to [21]. It will be shown that the angular dependences of the absorption of quasitransverse vibrational modes are qualitatively different in cubic crystals with the positive and the negative anisotropy of the second-order elasticity moduli.…”

Acoustoelectric charge transport at the LaAlO3/SrTiO3 interface

“…27 The strong temperature dependence of the latter 31 in STO leads to a much higher conversion efficiency of RF power into SAWs at the IDTs at lower temperature. In part, the higher SAW transmission signal could also be related to the reduced interaction of the thermally excited phonons with the acoustic waves in the crystal at lower temperatures, known as the Landau-Rumer mechanism, 32 resulting in reduced SAW attenuation during transit between input and output IDT. Additionally, we note that the SAW resonance frequency shifts to higher frequency at lower temperature.…”

Complex oxide acousto-electronics

“…This memory effect becomes much more pronounced at 150 K, as seen in Figure 5.1(e). Under application of 20 V dc bias on both IDTs, SAW transmission is again observed at 150 K, with an increased intensity as compared to the room temperature experiment, due to (i) the increased dielectric constant and thus higher electrostriction and (ii) reduced phonon scattering during SAW transmission 44,50,51,56 . In addition, the resonance frequency of the device shifted to 665 MHz at 150 K, due to the increase in sound velocity of the medium at lower temperatures 49 .…”

“…The strong temperature dependence of the latter 50 in STO leads to a much higher conversion efficiency of RF power into SAWs at the IDTs at lower temperature. In part, the higher SAW transmission signal also could be related to the reduced interaction of the thermally excited phonons with the acoustic waves in the crystal at lower temperatures, known as the Landau-Rumer mechanism 51 , resulting in reduced SAW attenuation during transit between input and output IDT.…”