Journal articles on the topic 'Diffusion Brillouin stimulée'
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1
Botineau, Jean, Claude Leycuras, Carlos Montes, and Eric Picholle. "Diffusion Brillouin stimulee dans un laser en anneau à fibre optique." Annales Des Télécommunications 44, no. 3-4 (March 1989): 173–78. http://dx.doi.org/10.1007/bf02997812.
2
Levasseur, Valérie. "Le libre accès : nouveau paradigme de diffusion des savoirs." Revue Organisations & territoires 27, no. 2 (December 1, 2018): 111–15. http://dx.doi.org/10.1522/revueot.v27n2.875.
Abstract:
Le libre accès est un mouvement qui prône l’accès gratuit pour tous aux connaissances et auxrésultats issus de la recherche sans barrière d’utilisation. Dans un monde où une grande partie de la rechercheest subventionnée par des fonds publics, il s’avère logique et essentiel que les résultats de cette recherchepuissent profiter à l’ensemble de la population. Plusieurs voies s’offrent aux auteurs désirant diffuser en libreaccès les résultats de leurs recherches et, peu importe la voie empruntée, les avantages sont indéniables, autantpour les utilisateurs que pour les auteurs eux-mêmes. L’avantage majeur du libre accès aux savoirs est qu’ilpermet une plus grande mise en application des résultats de la recherche et stimule l’innovation.
3
Neogi, A. "Stimulated Brillouin scattering in diffusion-driven semiconductors." Journal of the Optical Society of America B 11, no. 11 (November 1, 1994): 2246. http://dx.doi.org/10.1364/josab.11.002246.
4
Beugnot, Jean-Charles, Philippe Djemia, and Jérémie Margueritat. "Centenaire de la découverte de l’effet Brillouin." Photoniques, no. 114 (2022): 26–29. http://dx.doi.org/10.1051/photon/202111426.
Abstract:
En 1922, Léon Brillouin publie seul et en français, dans les comptes rendus de physique un article sur la diffusion de la lumière par des ondes acoustiques d’origine thermique. Il démontre que ces ondes acoustiques induisent un décalage en fréquence de la lumière diffusée. L'invention des lasers a rendu cette diffusion très efficace et permis de nombreux développements technologiques et industriels en spectroscopie des matériaux, microscopie médicale, lasers et capteurs distribués à fibres optiques.
5
Luo, Kuo, Biwei Wang, Nan Guo, Kuanglu Yu, Changyuan Yu, and Chao Lu. "Enhancing SNR by Anisotropic Diffusion for Brillouin Distributed Optical Fiber Sensors." Journal of Lightwave Technology 38, no. 20 (October 15, 2020): 5844–52. http://dx.doi.org/10.1109/jlt.2020.3004129.
6
Leonenko, N. N., I. Papić, A. Sikorskii, and N. Šuvak. "Ehrenfest–Brillouin-type correlated continuous time random walk and fractional Jacobi diffusion." Theory of Probability and Mathematical Statistics 99 (February 27, 2020): 137–47. http://dx.doi.org/10.1090/tpms/1086.
7
FISCHER, M., B. BONELLO, A. POLIAN, and A. ZAREMBOWITCH. "DÉTERMINATION DES VITESSES ULTRASONORES DANS LES TRÈS PETITS ÉCHANTILLONS PAR DIFFUSION BRILLOUIN." Le Journal de Physique Colloques 51, no. C2 (February 1990): C2–45—C2–48. http://dx.doi.org/10.1051/jphyscol:1990211.
8
KAUP, D. J., J. O. EL-REEDY, and GARY E. THOMAS. "Parametric interactions inside a magnetron." Journal of Plasma Physics 64, no. 4 (October 2000): 489–506. http://dx.doi.org/10.1017/s0022377800008783.
Abstract:
The purpose of this work is to understand theoretically what are the possible noise levels in a magnetron or a crossed-field amplifier (CFA), due to parametric three-wave interactions in the electron plasma, at various operating parameters. Our approach is to use the cold-fluid equations and their Fourier decomposition into a background (DC) mode, a pump (RF) mode, and two other noise (RF) modes. The two RF noise modes are assumed to interact parametrically with the large RF pump mode, and to satisfy the standard resonance conditions for the sum of the wave vectors and sum of the frequencies. We use our previous results to determine the background mode and the RF pump mode. Any strong RF electric field propagating in a crossed-field electron vacuum device can drive a Brillouin sheath unstable by means of a Rayleigh instability, whenever a wave–particle resonance can be found inside the sheath. What happens physically is that, at the resonance, the laminar flow of the electrons is strongly disturbed, and a diffusion process ensues, whereby the electrons diffuse away from the resonance region. This upsets the balance in the Brillouin flow, causing the electrons to redistribute into a new average DC density profile – which may be far from the original Brillouin profile, but is a stationary solution of a nonlinear diffusion equation. Using these stationary density profiles, we can then study the propagation of small RF signals on such a DC background, as well as their parametric interactions with the RF pump wave, at various DC voltages and magnetic fields. In addition to being able to predict the operating regime and the DC current flow, these studies demonstrate that parametric interactions probably limit the operating voltage range of a typical magnetron or crossed-field amplifier to about 20% above the Hartree voltage.
9
Marini, Samuel, Felipe B. Rizzato, and Renato Pakter. "Effects of the magnetic field penetration into the metal on the Brillouin flow in a crossed-field gap." Physics of Plasmas 30, no. 1 (January 2023): 012107. http://dx.doi.org/10.1063/5.0125449.
Abstract:
In this paper, the relativistic Brillouin flow in a crossed-field gap is investigated. For this, the case of a planar magnetron is considered. In contrast to previous studies, it is assumed that the electron discharge occurs in a timescale that is long compared to the magnetic diffusion time in the metal. It is found that the Brillouin flow properties and the overall scenario for the loss of magnetic insulation are different from the short pulse case. In particular, it is shown that two branches of equilibrium Brillouin flow solutions can coexist inside the gap region: one linearly stable and the other linearly unstable. As the parameters are varied, the two branches coalesce and cease to exist in a bifurcation that leads to a complete loss of magnetic insulation. Nevertheless, the mere existence of the unstable solution inside the gap is shown to affect the electron dynamics causing cathode–anode currents. An expression for the onset of the unstable solution is obtained and compared to the relativistic Hull cutoff condition for the short pulse case. It is found that the loss of magnetic insulation occurs for lower accelerating potentials in the present case. This effect is noticeable even for weakly relativistic cases.
10
Russo, D., A. Orecchini, A. De Francesco, F. Formisano, A. Laloni, C. Petrillo, and F. Sacchetti. "Brillouin Neutron Spectroscopy as a Probe to Investigate Collective Density Fluctuations in Biomolecules Hydration Water." Spectroscopy: An International Journal 27 (2012): 293–305. http://dx.doi.org/10.1155/2012/671265.
Abstract:
The role of water in the behaviour of biomolecules is well recognized. The coupling of motions between water and biomolecules has been studied in a wide time scale for theselfpart whilecollectivedynamics is still quite unexplored.Self-dynamics provides information about the diffusion processes of water molecules and relaxation processes of the protein structure.Collectivedensity fluctuations might provide important insight on the transmission of information possibly correlated to biological functionality. The idea that hydration water layers surrounding a biological molecule show aself-dynamical signature that differs appreciably from that of bulk water, in analogy with glass-former systems, is quite accepted. In the same picture Brillouin terahertz spectroscopy has been used to directly probecollectivedynamics of hydration water molecules around biosystems, showing a weaker coupling and a more bulklike behaviour. We will discuss results of collective modes of hydration water, arising from neutron Brillouin spectroscopy, in the context of biomolecules-solvent interaction.
11
Müller, U., R. Bactavatchalou, J. Baller, M. Philipp, R. Sanctuary, B. Zielinski, P. Alnot, W. Possart, and J. K. Krüger. "Acoustic profilometry of interphases in epoxy due to segregation and diffusion using Brillouin microscopy." New Journal of Physics 10, no. 2 (February 21, 2008): 023031. http://dx.doi.org/10.1088/1367-2630/10/2/023031.
12
FUJITA, S., H. C. HO, and Y. OKAMURA. "QUANTUM THEORY OF THE SEEBECK COEFFICIENT IN METALS." International Journal of Modern Physics B 14, no. 21 (August 20, 2000): 2231–40. http://dx.doi.org/10.1142/s0217979200002107.
Abstract:
Based on the idea that different temperatures generate different carrier densities and the resulting diffusion causes the thermal emf, a new formula for the Seebeck coefficient S is obtained: [Formula: see text], where q, n, εF, [Formula: see text]. and [Formula: see text]. are respectively charge, carrier density, Fermi energy, density of states at ∊F and volume. Ohmic and Seebeck currents are fundamentally different in nature. This difference can cause significantly different transport behaviors. For a multi-carrier metal the Einstein relation between the conductivity and the diffusion coefficient does not hold in general. Seebeck (S) and Hall (RH) coefficients in noble metals have opposite signs. This is shown to arise from the Fermi surface having "necks" at the Brillouin boundary.
13
Börjesson, L. "Secondary relaxations due to fast-ion diffusion in AgI-rich borate glasses observed by Brillouin scattering." Physical Review B 36, no. 9 (September 15, 1987): 4600–4612. http://dx.doi.org/10.1103/physrevb.36.4600.
14
Becker, Erich, and Charles McLandress. "Consistent Scale Interaction of Gravity Waves in the Doppler Spread Parameterization." Journal of the Atmospheric Sciences 66, no. 5 (May 1, 2009): 1434–49. http://dx.doi.org/10.1175/2008jas2810.1.
Abstract:
Abstract The standard Doppler spread parameterization of gravity waves, which was proposed by C.-O. Hines and has been applied in a number of middle atmosphere general circulation models, is extended by the inclusion of all effects associated with vertical diffusion. Here the Wentzel–Kramers–Brillouin (WKB) approximation is employed to calculate the vertical propagation of the wave spectrum in the presence of wave damping. According to the scale interaction between quasi-stationary turbulence and the larger nonturbulent flow, all vertical diffusion applied to the resolved flow should damp the parameterized gravity waves as well. Hence, the unobliterated part of the gravity wave spectrum is subject to diffusive damping by the following processes: 1) the background diffusion derived from the model’s boundary layer vertical diffusion scheme, which may extend into the middle atmosphere, 2) molecular diffusion, and 3) the turbulent diffusion resulting from the truncation of the gravity wave spectrum by Doppler spreading, which thus feeds back on the unobliterated gravity waves. The extended Doppler spread parameterization is examined using perpetual July simulations performed with a mechanistic general circulation model. For reasonable parameter settings, the convergence of the potential temperature flux cannot be neglected in the sensible heat budget, especially in the thermosphere. Less gravity wave flux enters the model thermosphere when vertical diffusion is included, thus avoiding the need for artificial means to control the parameterized gravity waves in the upper atmosphere. The zonal wind in the tropical middle and upper atmosphere is found to be especially sensitive to gravity wave damping by diffusion.
15
MAZROUI, M'HAMMED, and YAHIA BOUGHALEB. "SURFACE DIFFUSION IN SYSTEMS OF INTERACTING BROWNIAN PARTICLES." International Journal of Modern Physics B 15, no. 16 (June 30, 2001): 2193–247. http://dx.doi.org/10.1142/s0217979201001649.
Abstract:
The paper reviews recent results on diffusive phenomena in two-dimensional periodic potential. Specifically, static and dynamic properties are investigated by calculating different correlation functions. Diffusion process is first studied for one-dimensional system by using the Fokker–Planck equation which is solved numerically by the matrix continued fraction method in the case of bistable potential. The transition from hopping to liquid-like diffusion induced by variation of some parameters is discussed. This study will therefore serve to demonstrate the influence of this form of potential. Further, an analytical approximation for the dc-conductivity is derived for a wide damping range in the framework of the Linear Response Theory. On the basis of this expression, calculations of the ac conductivity of two-dimensional system with Frenkel–Kontorova pair interaction in the intermediate friction regime is performed by using the continued fraction expansion method. The dc-conductivity expression is used to determine the rest of the development. By varying the density of mobile ions we discuss commensurability effects. To get information about the diffusion mechanism, the full width at half maximum λω(q), of the quasi-elastic line of the dynamical structure factor S(q,ω) is computed. The calculations are extended up to large values of q covering several Brillouin zones. The analysis of λω(q) with different parameters shows that the most probable diffusion process in good two-dimensional superionic conductors consists of a competition between a back correlated hopping in one direction and forward correlated hopping in addition to liquid-like motions in the other direction.
16
Booske, John H., Reid F. Cooper, and Ian Dobson. "Mechanisms for nonthermal effects on ionic mobility during microwave processing of crystalline solids." Journal of Materials Research 7, no. 2 (February 1992): 495–501. http://dx.doi.org/10.1557/jmr.1992.0495.
Abstract:
Models for nonthermal effects on ionic motion during microwave heating of crystalline solids are considered to explain the anomolous reductions of activation energy for diffusion and the overall faster kinetics noted in microwave sintering experiments and other microwave processing studies. We propose that radiation energy couples into low (microwave) frequency elastic lattice oscillations, generating a nonthermal phonon distribution that enhances ion mobility and thus diffusion rates. Viewed in this manner, it is argued that the effect of the microwaves would not be to reduce the activation energy, but rather to make the use of a Boltzmann thermal model inappropriate for the inference of activation energy from sintering-rate or tracer-diffusion data. A highly simplified linear oscillator lattice model is used to qualitatively explore coupling from microwave photons to lattice oscillations. The linear mechanism possibilities include resonant coupling to weak-bond surface and point defect modes, and nonresonant coupling to zero-frequency displacement modes. Nonlinear mechanisms such as inverse Brillouin scattering are suggested for resonant coupling of electromagnetic and elastic traveling waves in crystalline solids. The models suggest that nonthermal effects should be more pronounced in polycrystalline (rather than single crystal) forms, and at elevated bulk temperatures.
17
Monthus, Cécile. "Large deviations for trajectory observables of diffusion processes in dimension d > 1 in the double limit of large time and small diffusion coefficient." Journal of Statistical Mechanics: Theory and Experiment 2024, no. 1 (January 1, 2024): 013205. http://dx.doi.org/10.1088/1742-5468/ad1390.
Abstract:
Abstract For diffusion processes in dimension d > 1, the statistics of trajectory observables over the time-window [ 0 , T ] can be studied via the Feynman–Kac deformations of the Fokker–Planck generator, which can be interpreted as Euclidean non-Hermitian electromagnetic quantum Hamiltonians. It is interesting to compare the four regimes corresponding to the time T, either finite or large, and to the diffusion coefficient D, either finite or small. (1) For finite T and finite D, one needs to consider the full time-dependent quantum problem that involves the full spectrum of the Hamiltonian. (2) For large time T → + ∞ and finite D, one only needs to consider the ground-state properties of the quantum Hamiltonian to obtain the generating function of rescaled cumulants and to construct the corresponding canonical conditioned processes. (3) For finite T and D → 0, one only needs to consider the dominant classical trajectory and its action satisfying the Hamilton–Jacobi equation, as in the semi-classical Wentzel–Kramers–Brillouin (WKB) approximation of quantum mechanics. (4) In the double limit T → + ∞ and D → 0, the simplifications in the large deviations in T D of trajectory observables can be analyzed via the two orders of limits, i.e. either from the limit D → 0 of the ground-state properties of the quantum Hamiltonians of (2), or from the limit of long classical trajectories T → + ∞ in the semi-classical WKB approximation of (3). This general framework is illustrated in dimension d = 2 with rotational invariance.
18
Shapovalov, Alexander, and Andrey Trifonov. "Approximate Solutions and Symmetry of a Two-Component Nonlocal Reaction-Diffusion Population Model of the Fisher–KPP Type." Symmetry 11, no. 3 (March 12, 2019): 366. http://dx.doi.org/10.3390/sym11030366.
Abstract:
We propose an approximate analytical approach to a ( 1 + 1 ) dimensional two-component system consisting of a nonlocal generalization of the well-known Fisher–Kolmogorov–Petrovskii– Piskunov (KPP) population equation and a diffusion equation for the density of the active substance solution surrounding the population. Both equations of the system have terms that describe the interaction effects between the population and the active substance. The first order perturbation theory is applied to the system assuming that the interaction parameter is small. The Wentzel–Kramers–Brillouin (WKB)–Maslov semiclassical approximation is applied to the generalized nonlocal Fisher–KPP equation with the diffusion parameter assumed to be small, which corresponds to population dynamics under certain conditions. In the framework of the approach proposed, we consider symmetry operators which can be used to construct families of special approximate solutions to the system of model equations, and the procedure for constructing the solutions is illustrated by an example. The approximate solutions are discussed in the context of the released activity effect variously debated in the literature.
19
Azad, Abul Kalam. "Robust Signal Denoising Techniques for Highly Accurate and Spatial Resolution Preserved Brillouin Optical Time Domain Analysis Sensors." Dhaka University Journal of Applied Science and Engineering 7, no. 2 (April 4, 2023): 31–38. http://dx.doi.org/10.3329/dujase.v7i2.65092.
Abstract:
The diminution of measurement uncertainty to an acceptable level and the preservation of experimental spatial resolution are highly desirable in many real-world applications of Brillouin optical time domain analysis (BOTDA) sensors. In practical applications of such sensors, the measurement uncertainty essentially relies upon the signal-to-noise ratio (SNR) of the experimental Brillouin gain spectra (BGSs) obtained throughout the sensing fiber. The improvement of such SNR using improper signal denoising techniques alters the experimental spatial resolution of the BOTDA sensors. In this paper, the use of non-local means filter (NLMF) and anisotropic diffusion filter (ADF) is experimentally demonstrated to enhance the uncertainty in the measurement of temperature using BOTDA sensors. For this purpose, the BGSs along a 41 km fiber are collected by averaging several numbers of BOTDA-traces from BOTDA hardware setup. Such BGSs are first denoised by employing NLMF and ADF to improve the measurement SNR. The Brillouin frequency shifts (BFSs) of denoised BGSs are then extracted via curve fitting technique (CFT). The BFS distribution is finally mapped to temperature distribution depending on the known BFS-temperature relationship of the sensing fiber. The robustness of the used filters is analyzed rigorously in terms of SNRs of BGSs, uncertainty in temperature extraction, spatial resolution and runtime in signal processing. The results indicate that the utilization of NLMF and ADF can enhance the SNRs of BGSs up to the maximum of 15.64 dB and 13.53 dB, respectively. Consequently, the uncertainties in the temperature extraction can be reduced up to the maximum of 52.63% and 57.31% for using NLMF and ADF, respectively. Moreover, both NLMF and ADF can preserve the experimental spatial resolution of the BOTDA sensors and include insignificant runtime to CFT. Thus, NLMF and ADF can be considered as robust signal denoising techniques for highly accurate and spatial resolution preserved BOTDA sensors. DUJASE Vol. 7 (2) 31-38, 2022 (July)
20
Marchal, Olivier. "Extratropical Rossby Waves in the Presence of Buoyancy Mixing." Journal of Physical Oceanography 39, no. 11 (November 1, 2009): 2910–25. http://dx.doi.org/10.1175/2009jpo4139.1.
Abstract:
Abstract The propagation of Rossby waves on a midlatitude β plane is investigated in the presence of density diffusion with the aid of linear hydrostatic theory. The search for wave solutions in a vertically bounded medium subject to horizontal (vertical) diffusion leads to an eigenvalue problem of second (fourth) order. Exact solutions of the problem are obtained for uniform background stratification (N), and approximate solutions are constructed for variable N using the Wentzel–Kramers–Brillouin method. Roots of the eigenvalue relations for free waves are found and discussed. The barotropic wave of adiabatic theory is also a solution of the eigenvalue problem as this is augmented with density diffusion in the horizontal or vertical direction. The barotropic wave is undamped as fluid parcels in the wave move only horizontally and are therefore insensitive to the vortex stretching induced by mixing. On the other hand, density diffusion modifies the properties of baroclinic waves of adiabatic theory. In the presence of horizontal diffusion the baroclinic modes are damped but their vertical structure remains unaltered. The ability of horizontal diffusion to damp baroclinic waves stems from its tendency to counteract the deformation of isopycnal surfaces caused by the passage of these waves. The damping rate increases (i) linearly with horizontal diffusivity and (ii) nonlinearly with horizontal wavenumber and mode number. In the presence of vertical diffusion the baroclinic waves suffer both damping and a change in vertical structure. In the long-wave limit the damping is critical (wave decay rate numerically equal to wave frequency) and increases as the square roots of vertical diffusivity and zonal wavenumber. Density diffusion in the horizontal or vertical direction reduces the amplitude of the phase speed of westward-propagating waves. Observational estimates of eddy diffusivities suggest that horizontal and vertical mixing strongly attenuates baroclinic waves in the ocean but that vertical mixing is too weak to notably modify the vertical structure of the gravest modes.
21
Wang, Liang-Ling, Xiao-Jun Cui, and Nian-Qiao Liu. "Effect of He+ ion implantation on Rb+-K+ exchanged KTiOPO4 optical waveguide." Modern Physics Letters B 32, no. 24 (August 27, 2018): 1850288. http://dx.doi.org/10.1142/s0217984918502883.
Abstract:
We report on the effect of 500 keV He[Formula: see text] ion implantation with a fluence of [Formula: see text] ions/cm2 on Rb[Formula: see text]-K[Formula: see text] ion exchanged KTiOPO4 optical waveguide. The refractive index distribution after ion implantation, ion exchange, and ion implantation and subsequent ion exchange were reconstructed by reflectivity calculation method, inverse Wentzel–Kramers–Brillouin, and intensity calculation method, respectively. The near field intensity distribution of the waveguides was simulated by Beam Propagation Method. The phase analysis of the samples was measured by X-ray diffraction technique. The damage layer formed in the depth of maximum nuclear energy deposition by ion implantation acts as a barrier to block the ions diffusion into the sample. Results exhibit that ion implantation and subsequent ion exchange are effective means for optical waveguide formation.
22
Anishchik, Victor M., Valiantzina A. Harushka, Uladzimir A. Pilipenka, Vladimir V. Ponariadov, Vitali A. Saladukha, and Anna A. Omelchenko Omelchenko. "Variation of the silicon optical parameters after rapid heat treatment." Journal of the Belarusian State University. Physics, no. 3 (September 29, 2021): 81–85. http://dx.doi.org/10.33581/2520-2243-2021-3-81-85.
Abstract:
The results of the effect of rapid heat treatment on the optical characteristics of a silicon wafer surface in the region of the G-point in the Brillouin zone are presented for different types of silicon wafers conductivity, their doping level, the covalent radii of dopants and the crystallographic orientation of the wafer surface. The absorption coefficient and refractive index of the initial 100 mm diameter samples KDB-12 <100>, KDB-10 <111>, KDB-0.005 <100> and KES-0.015 <100>, underwent standard chemical-mechanical polishing, was measured on a Uvisel 2 ellipsometer (Horiba Scientific, France) in the spectral range 0.6–6.0 eV (200–2100 nm) before and after rapid heat treatment. The incidence angle of the light beam was 70° relative to the sample plane. It is shown that the changes in the optical characteristics of the silicon surface in the spectral region of the location of the G-point in the Brillouin zone after rapid heat treatment is due to a decrease in the surface deformation potential due to solid-phase recrystallisation of the mechanically damaged layer. It has been established that carrying out the rapid heat treatment of silicon samples with a high boron concentration leads to a more significant decrease in the refractive index and absorption compared with silicon with a low boron concentration, due to an increase in the depletion of the silicon surface with boron as a result of diffusion processes at the silicon – silicon dioxide interface.
23
Indaleeb, Mustahseen M., and Sourav Banerjee. "Simultaneous Dirac-like Cones at Two Energy States in Tunable Phononic Crystals: An Analytical and Numerical Study." Crystals 11, no. 12 (December 7, 2021): 1528. http://dx.doi.org/10.3390/cryst11121528.
Abstract:
Simultaneous occurrence of Dirac-like cones at the center of the Brillouin zone (Γ) at two different energy states is termed Dual-Dirac-like cones (DDC) in this article. The occurrence of DDC is a rare phenomenon. Thus, the generation of multiple Dirac-like cones at the center of the Brillouin zone is usually non-manipulative and poses a challenge to achieve through traditional accidental degeneracy. However, if predictively created, DDC will have multiple engineering applications with acoustics and vibration. Thus, the possibilities of creating DDC have been identified herein using a simple square periodic array of tunable square phononic crystals (PnCs) in air media. It was found that antisymmetric deaf bands may play critical roles in tracking the DDC. Hence, pivoting on the deaf bands at two different energy states, an optimized tuning parameter was found to achieve Dirac-like cones at two distinct frequency states, simultaneously. Orthogonal wave transport identified as key Dirac phenomena was achieved at two frequencies, herein. It was identified that beyond the Dirac-like cone, the Dirac phenomena remain dominant when a doubly degenerated state created by a top band with positive curvature and a near-flat deaf band are lifted from a bottom band with negative curvature. Utilizing a mechanism of rotating the PnCs near a fixed deaf band, frequencies are tracked to form the DDC, and orthogonal wave transport is demonstrated. Exploiting the dispersion behavior, unique acoustic phenomena, such as ballistic wave transmission, pseudo diffusion and acoustic cloaking are also demonstrated at the Dirac frequencies using numerical simulation. The proposed tunable acoustic PnCs will have important applications in acoustic and ultrasonic imaging, waveguiding and even acoustic computing.
24
BONNET, J. E., M. G. MARTIN, J. AVILA, L. ROCA, and M. C. ASENSIO. "FIRST STAGE OF THE FORMATION OF SILVER THIN FILMS ON THE As-PASSIVATED Si(111)-(1×1) SURFACE." Surface Review and Letters 07, no. 01n02 (February 2000): 167–73. http://dx.doi.org/10.1142/s0218625x00000221.
Abstract:
The As-terminated Si surface has an ideally flat monolayer of As atoms at the outermost layer, showing a nonreconstructed (1×1) symmetry with one extra valence electron on each As atom, and setting a passivation, on the silicon surface, remarkable for its stablity up to temperatures above 600°C and under Ag deposition. Angle-resolved photoelectron spectroscopy (ARUPS) of valence bands in the main Brillouin zone directions of the As–Si(111) surface, and X-ray photoelectron diffraction (XPD), recorded with the LURE synchrotron light, provide the principal results presented in this work. No arsenic diffusion into the metallic overlayer is detected by photoemission, in a wide range of temperatures, proving the stability of the Ag/As–Si(111) interface, and allowing a first study of the structural and electronic properties of this flat interface. The formation of the silver–metal films on the semiconductor surface has been investigated, in particular the growth mode in the one-monolayer range and the building of the semiconductor–metal interface, and the evolution of the film during the silver deposition up to a few monolayers.
25
Kimura, Tomoaki, and Motohiko Murakami. "Fluid-like elastic response of superionic NH3 in Uranus and Neptune." Proceedings of the National Academy of Sciences 118, no. 14 (March 29, 2021): e2021810118. http://dx.doi.org/10.1073/pnas.2021810118.
Abstract:
Nondipolar magnetic fields exhibited at Uranus and Neptune may be derived from a unique geometry of their icy mantle with a thin convective layer on top of a stratified nonconvective layer. The presence of superionic H2O and NH3 has been thought as an explanation to stabilize such nonconvective regions. However, a lack of experimental data on the physical properties of those superionic phases has prevented the clarification of this matter. Here, our Brillouin measurements for NH3 show a two-stage reduction in longitudinal wave velocity (Vp) by ∼9% and ∼20% relative to the molecular solid in the temperature range of 1,500 K and 2,000 K above 47 GPa. While the first Vp reduction observed at the boundary to the superionic α phase was most likely due to the onset of the hydrogen diffusion, the further one was likely attributed to the transition to another superionic phase, denoted γ phase, exhibiting the higher diffusivity. The reduction rate of Vp in the superionic γ phase, comparable to that of the liquid, implies that this phase elastically behaves almost like a liquid. Our measurements show that superionic NH3 becomes convective and cannot contribute to the internal stratification.
26
Kheffache, Sedik, Rabah Chadli, and Antoine Khater. "Vibrational properties at the ordered metallic surface alloy system Au(110)-1×2-Pd." International Journal of Modern Physics B 30, no. 20 (August 10, 2016): 1650126. http://dx.doi.org/10.1142/s0217979216501265.
Abstract:
We present a calculation for the vibrational properties of the ordered surface alloy Au(110)-1×2-Pd on a crystalline substrate of Au. The surface phonon dispersion curves and the local vibrations densities of states (LDOS) are calculated in the harmonic approximation for the system, using the phase field matching theory (PFMT) method and associated real space Green’s functions. In particular, it is shown that the surface alloy presents optic vibrational modes above the Au bulk bands, along the directions of high-symmetry [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] of the corresponding two-dimensional Brillouin zone. Measurements of the surface phonon dispersion branches can hence be made by different techniques such as helium atom scattering (HAS) to compare with. The calculated LDOS for Au and Pd atomic sites in the four top surface atomic layers span a wider range of frequencies than those for the individual Au(110) or Pd(110) metallic surfaces. These LDOS provide a spectral signature for the progressive transition from the surface dynamics to that of the Au crystal bulk. Knowledge of these LDOS for the surface alloy can also serve as an input for modeling the diffusion and reaction rates of chemical species at its surface.
27
Park, Junho, Paul Billant, and Jong-Jin Baik. "Instabilities and transient growth of the stratified Taylor–Couette flow in a Rayleigh-unstable regime." Journal of Fluid Mechanics 822 (May 31, 2017): 80–108. http://dx.doi.org/10.1017/jfm.2017.254.
Abstract:
The stability of the Taylor–Couette flow is analysed when there is a stable density stratification along the axial direction and when the flow is centrifugally unstable, i.e. in the Rayleigh-unstable regime. It is shown that not only the centrifugal instability but also the strato-rotational instability can occur. These two instabilities can be explained and well described by means of a Wentzel–Kramers–Brillouin–Jeffreys asymptotic analysis for large axial wavenumbers in inviscid and non-diffusive limits. In the presence of viscosity and diffusion, numerical results reveal that the strato-rotational instability becomes dominant over the centrifugal instability at the onset of instability when the axial density stratification is sufficiently strong. Linear transient energy growth is next investigated for counter-rotating cylinders in the stable regime of the Froude number–Reynolds number parameter space. We show that there exist two types of transient growth mechanism analogous to the lift up and the Orr mechanisms in homogeneous fluids but with the additional effect of density perturbations. The dominant mechanism depends on the stratification: when the stratification is strong, non-axisymmetric three-dimensional perturbations achieve the optimal energy growth through the Orr mechanism while for moderate stratification, axisymmetric perturbations lead to the optimal transient growth by a lift-up mechanism involving internal waves.
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Jung, Hakkee. "SPICE model of drain induced barrier lowering in sub-10 nm junctionless cylindrical surrounding gate MOSFET." International Journal of Electrical and Computer Engineering (IJECE) 10, no. 2 (April 1, 2020): 1288. http://dx.doi.org/10.11591/ijece.v10i2.pp1288-1295.
Abstract:
We propose a SPICE Drain Induced Barrier Lowering (DIBL) model for sub-10 nm Junctionless Cylindrical Surrounding Gate (JLCSG) MOSFETs. The DIBL shows the proportionl relation to the -3 power of the channel length Lg and the 2 power of silicon thickness in MOSFET having a rectangular channel, but this relation cannot be used in cylindrical channel because of the difference in channel structure. The subthreshold currents, including the tunneling current from the WKB (Wentzel-Kramers-Brillouin) approximation as well as the diffusion-drift current, are used in the model. The constant current method is used to define the threshold voltage as the gate voltage at a constant current, (2πR/Lg)10-7 A for channel length and channel radius R. The central potential of the JLCSG MOSFET is determined by the Poisson equation. As a result, it can be seen that the DIBL of the JLCSG MOSFET is proportional to the –2.76 power of the channel length, to the 1.76 power of the channel radius, and linearly to the oxide film thickness. At this time, we observe that the SPICE parameter, the static feedback coefficient, has a value less than 1 1, and this model can be used to analyze the DIBL of the JLCSG MOSFET.
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Park, J., V. Prat, and S. Mathis. "Horizontal shear instabilities in rotating stellar radiation zones." Astronomy & Astrophysics 635 (March 2020): A133. http://dx.doi.org/10.1051/0004-6361/201936863.
Abstract:
Context. Rotational mixing transports angular momentum and chemical elements in stellar radiative zones. It is one of the key processes for modern stellar evolution. In the past two decades, an emphasis has been placed on the turbulent transport induced by the vertical shear instability. However, instabilities arising from horizontal shear and the strength of the anisotropic turbulent transport that they may trigger remain relatively unexplored. The weakest point of this hydrodynamical theory of rotational mixing is the assumption that anisotropic turbulent transport is stronger in horizontal directions than in the vertical one. Aims. This paper investigates the combined effects of stable stratification, rotation, and thermal diffusion on the horizontal shear instabilities that are obtained and discussed in the context of stellar radiative zones. Methods. The eigenvalue problem describing linear instabilities of a flow with a hyperbolic-tangent horizontal shear profile was solved numerically for a wide range of parameters. When possible, the Wentzel–Kramers–Brillouin–Jeffreys (WKBJ) approximation was applied to provide analytical asymptotic dispersion relations in both the nondiffusive and highly diffusive limits. As a first step, we consider a polar f-plane where the gravity and rotation vector are aligned. Results. Two types of instabilities are identified: the inflectional and inertial instabilities. The inflectional instability that arises from the inflection point (i.e., the zero second derivative of the shear flow) is the most unstable when at a zero vertical wavenumber and a finite wavenumber in the streamwise direction along the imposed-flow direction. While the maximum two-dimensional growth rate is independent of the stratification, rotation rate, and thermal diffusivity, the three-dimensional inflectional instability is destabilized by stable stratification, while it is stabilized by thermal diffusion. The inertial instability is rotationally driven, and a WKBJ analysis reveals that its growth rate reaches the maximum value of √f(1 − f) in the inviscid limit as the vertical wavenumber goes to infinity, where f is the dimensionless Coriolis parameter. The inertial instability for a finite vertical wavenumber is stabilized as the stratification increases, whereas it is destabilized by the thermal diffusion. Furthermore, we found a selfsimilarity in both the inflectional and inertial instabilities based on the rescaled parameter PeN2 with the Péclet number Pe and the Brunt–Väisälä frequency N.
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Challab, Nabil, Yves Roussigné, Salim Mourad Chérif, Mihai Gabor, and Mohamed Belmeguenai. "Magnetic Damping and Dzyaloshinskii–Moriya Interactions in Pt/Co2FeAl/MgO Systems Grown on Si and MgO Substrates." Materials 16, no. 4 (February 7, 2023): 1388. http://dx.doi.org/10.3390/ma16041388.
Abstract:
Spin-pumping-induced damping and interfacial Dzyaloshinskii–Moriya interaction (iDMI) have been studied in Pt/Co2FeAl/MgO systems grown on Si or MgO substrates as a function of Pt and Co2FeAl (CFA) thicknesses. For this, we combined vibrating sample magnetometry (VSM), microstrip ferromagnetic resonance (MS-FMR), and Brillouin light scattering (BLS). VSM measurements of the magnetic moment at saturation per unit area revealed the absence of a magnetic dead layer in both systems, with a higher magnetization at saturation obtained for CFA grown on MgO. The key parameters governing the spin-dependent transport through the Pt/CFA interface, including the spin mixing conductance and the spin diffusion length, have been determined from the CFA and the Pt thickness dependence of the damping. BLS has been used to measure the spin wave non-reciprocity via the frequency mismatch between the Stokes and anti-Stokes lines. iDMI has been separated from the contribution of the interface perpendicular anisotropy difference between Pt/CFA and CFA/MgO. Our investigation revealed that both iDMI strength and spin pumping efficiency are higher for CFA-based systems grown on MgO due to its epitaxial growth confirmed by MS-FMR measurements of the in-plane magnetic anisotropy. This suggests that CFA grown on MgO could be a promising material candidate as a spin injection source via spin pumping and for other spintronic applications.
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Hauck, Nicolas, Nalin Seixas, Silvia Centeno, Raimund Schlüßler, Gheorghe Cojoc, Paul Müller, Jochen Guck, Dominik Wöll, Ludger Wessjohann, and Julian Thiele. "Droplet-Assisted Microfluidic Fabrication and Characterization of Multifunctional Polysaccharide Microgels Formed by Multicomponent Reactions." Polymers 10, no. 10 (September 21, 2018): 1055. http://dx.doi.org/10.3390/polym10101055.
Abstract:
Polysaccharide-based microgels have broad applications in multi-parametric cell cultures, cell-free biotechnology, and drug delivery. Multicomponent reactions like the Passerini three-component and the Ugi four-component reaction are shown in here to be versatile platforms for fabricating these polysaccharide microgels by droplet microfluidics with a narrow size distribution. While conventional microgel formation requires pre-modification of hydrogel building blocks to introduce certain functionality, in multicomponent reactions one building block can be simply exchanged by another to introduce and extend functionality in a library-like fashion. Beyond synthesizing a range of polysaccharide-based microgels utilizing hyaluronic acid, alginate and chitosan, exemplary in-depth analysis of hyaluronic acid-based Ugi four-component gels is conducted by colloidal probe atomic force microscopy, confocal Brillouin microscopy, quantitative phase imaging, and fluorescence correlation spectroscopy to elucidate the capability of microfluidic multicomponent reactions for forming defined polysaccharide microgel networks. Particularly, the impact of crosslinker amount and length is studied. A higher network density leads to higher Young’s moduli accompanied by smaller pore sizes with lower diffusion coefficients of tracer molecules in the highly homogeneous network, and vice versa. Moreover, tailored building blocks allow for crosslinking the microgels and incorporating functional groups at the same time as demonstrated for biotin-functionalized, chitosan-based microgels formed by Ugi four-component reaction. To these microgels, streptavidin-labeled enzymes are easily conjugated as shown for horseradish peroxidase (HRP), which retains its activity inside the microgels.
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Strocov, V. N., F. Lechermann, A. Chikina, F. Alarab, L. L. Lev, V. A. Rogalev, T. Schmitt, and M.-A. Husanu. "Dimensionality of mobile electrons at x-ray-irradiated LaAlO3/SrTiO3 interfaces." Electronic Structure 4, no. 1 (February 4, 2022): 015003. http://dx.doi.org/10.1088/2516-1075/ac4e74.
Abstract:
Abstract Electronic structure of LaAlO3/SrTiO3 (LAO/STO) samples, grown at low oxygen pressure and post-annealed ex situ, was investigated by soft-x-ray ARPES focussing on the Fermi momentum (k F) of the mobile electron system (MES). X-ray irradiation of these samples at temperatures below 100 K creates oxygen vacancies (VOs) injecting Ti t 2g-electrons into the MES. At this temperature the oxygen out-diffusion is suppressed, and the VOs should appear mostly in the top STO layer. The x-ray generated MES demonstrates, however, a pronounced three-dimensional (3D) behavior as evidenced by variations of its experimental k F over different Brillouin zones. Identical to bare STO, this behavior indicates an unexpectedly large extension of the x-ray generated MES into the STO depth. The intrinsic MES in the standard LAO/STO samples annealed in situ, in contrast, demonstrates purely two-dimensional (2D) behaviour. The relevance of our ARPES data analysis is supported by model calculations to compare the intensity vs gradient methods of the k F determination as a function of the energy resolution ratio to the bandwidth. Based on self-interaction-corrected DFT calculations of the MES induced by VOs at the interface and in STO bulk, we discuss possible scenarios of the puzzling 3D-ity. It may involve either a dense ladder of quantum-well states formed in a long-range interfacial potential or, more likely, x-ray-induced bulk metallicity in STO accessed in the ARPES experiment through a short-range interfacial barrier. The mechanism of this metallicity may involve remnant VOs and photoconductivity-induced metallic states in the STO bulk, and even more exotic mechanisms such as x-ray induced formation of Frenkel pairs.
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Seong, Hyangsuk, and S. D. Mahanti. "Ionic Overlayers on Corrugated Surfaces III : Dynamics in the Fluid Phase." MRS Proceedings 291 (January 1, 1992). http://dx.doi.org/10.1557/proc-291-303.
Abstract:
ABSTRACTUsing molecular dynamics simulation, we have studied the dynamics in the fluid phase of ionic overlayers on corrugated substrates. This is a good model to probe the dynamics of intercalants inside the galleries of intercalated systems. We have calculated the diffusion constant from the incoherent dynamic structure factor, de Genne oscillations in the q-dependence of the Rayleigh peak width and dispersion of Brillouin peaks have been obtained from the coherent dynamic structure factor. These results are compared with neutron scattering measurements in stage-2 RbC24 and earlier simulation results.
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Pacaud, Jérôme, Franck Martin, Anny Michel, Christiane Jaouen, Philippe Djemia, and François Ganot. "Structural and Elastic Response of Mo/Ni Multilayers to Ion Irradiation." MRS Proceedings 615 (2000). http://dx.doi.org/10.1557/proc-615-g8.7.1.
Abstract:
ABSTRACTMo/Ni multilayers are investigated by x-ray diffraction and Brillouin light scattering before and after ion induced stress relaxation and mixing. Study of the evolution of interplanar distances in both layers as a function of the period exhibits a strong anomaly of the Mo (110) distance (in the growth direction) that can be correlated with the elastic anomaly. The very low interplanar distance in the molybdenum layers found after stress relaxation seems to favor an explanation of this behavior based on the diffusion of Ni in the Mo layers during the growth.
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Tian, Liang, Wei E. I. Sha, Hao Xie, Dongxue Liu, Tian-Ge Sun, Yin-Shui Xia, and Wenchao Chen. "Carrier transport simulation methods for electronic devices with coexistence of quantum transport and diffusive transport." Journal of Applied Physics 135, no. 22 (June 11, 2024). http://dx.doi.org/10.1063/5.0209479.
Abstract:
In this manuscript, carrier transport simulation methods are proposed for devices with the coexistence of quantum transport and diffusive transport by combining the nonequilibrium Green's function method with the drift-diffusion transport simulation method. Current continuity between quantum transport and drift-diffusion transport is ensured by setting quantum transport current as the connection boundary condition of drift-diffusion simulation or by introducing quantum transport-induced carrier generation rates to drift-diffusion simulation. A comprehensive study of our method and the method combining the Wentzel–Kramers–Brillouin (WKB) method with the drift-diffusion transport simulation method is performed for n-type tunnel oxide passivating contact solar cell to investigate their applicable conditions and balance the accuracy and computational cost. As the oxide barrier width, barrier height, and electron effective mass increase, or the doping concentration in the electron transport layer decreases to the extent that the blocking effect of the oxide barrier on light-generated electrons becomes significant, method I is more accurate since the transmission coefficient near the conduction band edge calculated by WKB is overestimated; otherwise, method II is more suitable due to its low computational cost without the loss of accuracy. In addition, the differences between current densities, carrier densities, and Shockley–Read–Hall recombination rates simulated under the two current continuity conditions for the solar cell with different carrier mobilities are also further explored and analyzed.
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Huang, Qiang-Kai-Lai, Yun-Kai Liu, Pei-Chao Cao, Xue-Feng Zhu, and Ying Li. "Two-Dimensional Thermal Regulation Based on NonHermitian Skin Effect." Chinese Physics Letters, August 31, 2023. http://dx.doi.org/10.1088/0256-307x/40/10/106601.
Abstract:
Abstract The non-Hermitian skin effect has been applied in multiple fields. However, there are relatively few models in the field of thermal diffusion that utilize the non-Hermitian skin effect for achieving thermal regulation. Here, we propose two non-Hermitian Su-Schrieffer-Heeger (SSH) models for thermal regulation: one capable of achieving edge states, and the other capable of achieving corner states within the thermal field. By analyzing the energy band structures and the generalized Brillouin zone, we predict the appearance of the non-Hermitian skin effect in these two models. Furthermore, we analyze the time-dependent evolution results and assess the robustness of the models. The results indicate that the localized thermal effects of the models align with our predictions. In summary, this work presents two models based on the non-Hermitian skin effect for regulating the thermal field, injecting vitality into the design of non-Hermitian thermal diffusion systems.
37
Adnan, Saqeeb, Amey Khanolkar, Shuxiang Zhou, David H. Hurley, and Marat Khafizov. "Optical pulse-induced ultrafast antiferrodistortive transition in SrTiO3." Applied Physics Reviews 11, no. 3 (July 2, 2024). http://dx.doi.org/10.1063/5.0194334.
Abstract:
The ultrafast dynamics of the antiferrodistortive phase transition in perovskite SrTiO3 is monitored via time-domain Brillouin scattering. Using femtosecond optical pulses, we initiate a thermally driven tetragonal-to-cubic structural transformation and detect the crystal phase through changes in the frequency of Brillouin oscillations (BO) induced by propagating acoustic phonons. Coupling the measured BO frequency with a spatiotemporal heat diffusion model, we demonstrate that, for a sample kept in the tetragonal phase, deposition of sufficient thermal energy induces a rapid transformation of the heat-affected region to the cubic phase. The initial phase change is followed by a slower reverse cubic-to-tetragonal phase transformation occurring on a timescale of hundreds of picoseconds. We attribute this ultrafast phase transformation in the perovskite to a structural resemblance between atomic displacements of the R-point soft optic mode of the cubic phase and the tetragonal phase, both characterized by anti-phase rotation of oxygen octahedra. The structural relaxation time exhibits a strong temperature dependence consistent with the prediction of the equation of motion describing collective oxygen octahedra rotation based on the energy landscape of the phenomenological Landau theory of phase transitions. Evidence of such a fast structural transition in perovskites can open up new avenues in information processing and energy storage sectors.
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Wu, Lei, and Xiao-Jun Gu. "On the accuracy of macroscopic equations for linearized rarefied gas flows." Advances in Aerodynamics 2, no. 1 (January 8, 2020). http://dx.doi.org/10.1186/s42774-019-0025-4.
Abstract:
AbstractMany macroscopic equations are proposed to describe the rarefied gas dynamics beyond the Navier-Stokes level, either from the mesoscopic Boltzmann equation or some physical arguments, including (i) Burnett, Woods, super-Burnett, augmented Burnett equations derived from the Chapman-Enskog expansion of the Boltzmann equation, (ii) Grad 13, regularized 13/26 moment equations, rational extended thermodynamics equations, and generalized hydrodynamic equations, where the velocity distribution function is expressed in terms of low-order moments and Hermite polynomials, and (iii) bi-velocity equations and “thermo-mechanically consistent" Burnett equations based on the argument of “volume diffusion”. This paper is dedicated to assess the accuracy of these macroscopic equations. We first consider the Rayleigh-Brillouin scattering, where light is scattered by the density fluctuation in gas. In this specific problem macroscopic equations can be linearized and solutions can always be obtained, no matter whether they are stable or not. Moreover, the accuracy assessment is not contaminated by the gas-wall boundary condition in this periodic problem. Rayleigh-Brillouin spectra of the scattered light are calculated by solving the linearized macroscopic equations and compared to those from the linearized Boltzmann equation. We find that (i) the accuracy of Chapman-Enskog expansion does not always increase with the order of expansion, (ii) for the moment method, the more moments are included, the more accurate the results are, and (iii) macroscopic equations based on “volume diffusion" do not work well even when the Knudsen number is very small. Therefore, among about a dozen tested equations, the regularized 26 moment equations are the most accurate. However, for moderate and highly rarefied gas flows, huge number of moments should be included, as the convergence to true solutions is rather slow. The same conclusion is drawn from the problem of sound propagation between the transducer and receiver. This slow convergence of moment equations is due to the incapability of Hermite polynomials in the capturing of large discontinuities and rapid variations of the velocity distribution function. This study sheds some light on how to choose/develop macroscopic equations for rarefied gas dynamics.
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Masuda, Hiroshi, Daiki Tamao, and Hidehiro Yoshida. "Ab initio study of electric field effects on phonon vibrations in tetragonal ZrO2." Applied Physics Letters 123, no. 2 (July 10, 2023). http://dx.doi.org/10.1063/5.0154894.
Abstract:
The effects of external electric fields on phonon-associated phenomena, such as phase transformation and diffusion in ZrO2 ceramics, have been reported from recent experiments. This study examined the effects of external direct current (DC) electric fields on the phonon vibration properties in a tetragonal ZrO2 unit cell based on the density-functional perturbation theory. Phonon dispersions and densities of states were analyzed with optimized structures under varying external DC electric fields up to 45 mV/Å. The field sensitivities of phonon characteristics exhibited significant orientation dependence and were attributed to ionic polarization associated with symmetry breaking in dielectric properties. Optical phonons showed considerable field sensitivities particularly near the Brillouin zone boundaries, such as in the M (π/a, π/a, 0) to X (0, π/a, 0) and A (π/a, π/a, π/c) to R (0, π/a, π/c) directions, where doubly degenerate phonon frequencies exhibited splitting behaviors associated with the symmetry breaking between two unique oxygen atoms in the original unit cell. In contrast, transversal acoustic phonons demonstrated a softening trend with increasing field strengths around the Z (0, 0, π/c) point, where imaginary and splitting frequencies were obtained under electric fields of >40 mV/Å, indicating the potential phase transformation from the tetragonal to orthorhombic symmetries under strong external electric fields.