Components Of Polarization Vector Research Articles

New physics and the tau polarization vector in b \u2192 mathrm{c}tau {overline{nu}}_{tau } decays

For a general Hb → {H}_ctau {overline{nu}}_{tau } decay we analyze the role of the τ polarization vector {mathcal{P}}^{mu } in the context of lepton flavor universality violation studies. We use a general phenomenological approach that includes, in addition to the Standard Model (SM) contribution, vector, axial, scalar, pseudoscalar and tensor new physics (NP) terms which strength is governed by, complex in general, Wilson coefficients. We show that both in the laboratory frame, where the initial hadron is at rest, and in the center of mass of the two final leptons, a overrightarrow{mathcal{P}} component perpendicular to the plane defined by the three-momenta of the final hadron and the τ lepton is only possible for complex Wilson coefficients, being a clear signal for physics beyond the SM as well as time reversal (or CP-symmetry) violation. We make specific evaluations of the different polarization vector components for the Λb → Λc, {overline{B}}_c → ηc, J/ψ and overline{B} → D(*) semileptonic decays, and describe NP effects in the complete two-dimensional space associated with the independent kinematic variables on which the polarization vector depends. We find that the detailed study of {mathcal{P}}^{mu } has great potential to discriminate between different NP scenarios for 0− → 0− decays, but also for Λb → Λc transitions. For this latter reaction, we pay special attention to corrections to the SM predictions derived from complex Wilson coefficients contributions.

Field-deformational effects in GPI ferroelectric materials

ABSTRACTThe effects appearing under the simultaneously applied mechanical stress and electric field are studied. We use a model of glycinium phosphite ferroelectric, modified by taking into account of piezoelectric coupling of the ordering structure elements with the lattice strains . Within the framework of two-particle cluster approximation, the components of polarization vector and the static dielectric permittivity tensor as well as piezoelectric and thermal characteristics are calculated. The separate and simultaneous effects of shear stress and electric field on the ferroelectric phase transition in the crystal are studied and mutually compared.

The effect of hydrostatic pressure on thermodynamic characteristics of NH3CH2COOH·H2PO3 type ferroelectric materials

The model of NH$_3$CH$_2$COOH$\cdot$H$_2$PO$_3$, modified by taking into account the piezoelectric coupling between the ordering structure elements and the strains $\varepsilon_i$, $\varepsilon_j$, is used for investigation of the effects that appear under external pressures. Within two-particle cluster approximation, the components of polarization vector and static dielectric permittivity tensor of the mechanically clamped and free crystals, their piezoelectric and thermal characteristics are calculated. The effect of hydrostatic pressure on the phase transition and the calculated physical characteristics of the crystal is studied. A good quantitative description of experimental data for these crystals is obtained.

Measurement of the polarization vector in BiMnO3 multiferroic thin films using surface and embedded microelectrodes

We present a technique for resolving multiple spatial components of the remanent polarization vectors in thin film ferroelectrics. Using complementary electrode configurations of surface and embedded interdigital microelectrode arrays, both the in-plane and out-of-plane polarizations were measured independently. As a result, we found that the ferroelectric polarization vector was 16% larger than what typical measurement geometries would report. The spatial sensitivity exhibited by the method presented here is crucial to identifying novel coupling mechanisms which lead to modified ferroelectric polarization vector components.

Analysis of dual-mode thin film bulk acoustic resonators based on polar c-axis tilted wurtzite gallium nitride

We present the analytical study of dual-mode thin film bulk acoustic resonators (FBARs) based on wurtzite gallium nitride (GaN) thin films with tilted c-axis orientation. The normal-plane and in-plane electric polarization vector components caused by the titled c-axis orientation induce the coexistence of the thickness longitudinal and thickness shear modes in the thin film resonator. Due to the c-axis orientation dependency of material properties including elastic stiffness, dielectric constants, and piezoelectric coefficients, bulk wave properties of FBARs including acoustic velocity and electromechanical coupling coefficient, and electrical impedance spectra are greatly affected by the tilt angle. It is found that the pure longitudinal mode occurs at θ=0° and 66.4°, and the pure shear mode occurs at θ=42.8° and 90°. In addition, the electromechanical coupling coefficient for thickness shear mode has a maximum value 3.18% at θ=34.2°, which is larger than the maximum value for pure thickness longitudinal mode 2.44% at θ=0°. The calculation results show that FBARs based on tilted c-axis wurtzite GaN thin films are promising for frequency control device design and applications.

The effect of transverse electric fields on dielectric, piezoelectric, elastic and thermal properties of the Rochelle salt NaKC_{4}H_{4}O_{6} · 4H_{2}O

Modied four-sublattice model for Rochelle salt by taking into account piezoelectric interactions with shear strain "4, "5 and "6 is proposed. Components of polarization vector and static dielectric permittivity tensor for both mechanically clamped and free crystals, their piezoelectric characteristics and elastic modules are derived in the mean eld approximation. A comprehensive study of transverse eld effect on phase transition temperatures, dielectric and elastic properties of Rochelle salt has been performed for the rst time.

Fuzzy simultaneous measurement of two polarization vector components

The advent of quantum computers threatens the security of conventional encryption schemes (e.g., those based upon the excessive amount of computational time that might be required to guess your password). Quantum encryption is intended to restore the security by basing it instead upon the impossibility of the simultaneous measurement of two noncommuting operators. I derive a measurement associated with the angular momentum lowering operator, which describes a simultaneous (yet realizable) measurement of two noncommuting spin-vector components. Correlations between two such detectors are also discussed and compared with the conventional Stern-Gerlach results.

Supression of size effects in ferroelectric films

It is widely reported that the dielectric permittivity of ferroelectric films decreases with decreasing film thickness, and understanding and controlling these size effects are very important for charge storage application of these films. By combining phenomenological theory with careful experimental work, we have shown that the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films. We have taken two extreme boundary conditions to prove our point. For the case normal electrodes, it is assumed that the boundary condition for the component of polarization vector at the ferroelectric/electrode interface is P = 0. This case corresponds to the presence of a strong edge field, resulting in “freezing out” of the ferroelectric polarization at the interface and thus exhibiting severe size effects. However, if one utilizes conductive oxide electrodes that are ferroelectric in nature the polarization would not vanish at the ferroelectric/electrode interface and therefore the size effects are largely suppressed. To prove our point and to eliminate grain size, stress, and compositional effects, epitaxial SrTiO3 thin films with stoichiometric composition on SrTiO3 single crystal substrates were investigated. In fact, the experimental data also indicates that the use of ferroelectric electrodes indeed suppresses the size effects.

Suppression of Size Effects in Ferroelectric Films

AbstractIt is widely reported that the dielectric permittivity of ferroelectric films decreases with decreasing film thickness, and understanding and controlling these size effects are very important for charge storage application of these films. By combining phenomenological theory with careful experimental work, we have shown that the form of the boundary condition for the polarization plays a decisive role in the manifestation of size effects in ferroelectric films. We have taken two extreme boundary conditions to prove our point. For the case normal electrodes, it is assumed that the boundary condition for the component of polarization vector at the ferroelectric/electrode interface is P = 0. This case corresponds to the presence of a strong edge field, resulting in “freezing out” of the ferroelectric polarization at the interface and thus exhibiting severe size effects. However, if one utilizes conductive oxide electrodes that are ferroelectric in nature the polarization would not vanish at the ferroelectric/electrode interface and therefore the size effects are largely suppressed. To prove our point and to eliminate grain size, stress, and compositional effects, epitaxial SrTiO3 thin films with stoichiometric composition on SrTiO3 single crystal substrates were investigated. In fact, the experimental data also indicates that the use of ferroelectric electrodes indeed suppress the size effects.

Semi-infinite optimization formulation to obtain accurate phenomenological models for all phases of ferroelectric-ferroelastic crystals

A formulation based on semi-infinite optimization is proposed to obtain accurate thermodynamic phenomenological models over all phases of ferroelectric and ferroelastic materials. The formulation is illustrated with barium titanate (BaTiO/sub 3/) single crystals. Analogous to the Devonshire theory, the elastic Gibbs function is expressed as a truncated Taylor series in terms of the polarization vector components, whose coefficients are unknown functions of temperature. Employing a methodology based on semi-infinite optimization, the unknown coefficients are determined using experimental measurements. In contrast to all existing methods in the literature, the methodology proposed herein yields models that accurately predict the ferroelectric properties such as phase transitions, spontaneous polarization, and permittivity over a large temperature range. The objective function-which is a measure of the relative error in the phenomenological model-for the optimal model shows a difference of more than 500% over the models obtained using previously proposed methods.

The need of electron microscopy in the study of domains and domain walls in ferroelectrics

Domain structures play a key role in determining the physical properties of ferroelectric materials. The formation of these ferroelectric domains and domain walls are determined by the intrinsic nonlinearity and the nonlocal coupling of the polarization. Analogous to soliton excitations, domain walls can have high mobility when the domain wall energy is high. The domain wall can be describes by a continuum theory owning to the long range nature of the dipole-dipole interactions in ferroelectrics. The simplest form for the Landau energy is the so called ϕ model which can be used to describe a second order phase transition from a cubic prototype,where Pi (i =1, 2, 3) are the components of polarization vector, α's are the linear and nonlinear dielectric constants. In order to take into account the nonlocal coupling, a gradient energy should be included, for cubic symmetry the gradient energy is given by,

Neutron depolarization in matter with polarized nuclei

The influence of fluctuations of a nuclear pseudomagnetic field on neutron spin rotation in matter with polarized nuclei is described. It is shown that nuclear pseudomagnetic field fluctuations lead to neutron spin depolarization. It is also shown that the attenuation of the polarization vector components of a neutron as a function of target thickness is described by a nonexponential law.