Certain questions of the theory of polarization of polar dielectrics

An analysis is presented in this paper of the theory of polarization of polar dielectrics, among which is a broad circle of polymers, in order to set up a method of estimating the dipole correlation factor of the substance under investigation without using the method of dilute solutions. It is shown that a strict computation of the field acting on the molecule results in a formula for the dispersion of the substance corresponding to test results. The formula permits estimation of the parameter of an empirical relationship describing the temperature history of the dipole correlation factor.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 56–62, January, 1976.     

Relaxational polarization of dielectrics

Conclusion It follows from the foregoing that the main equations for the static and complex dielectric permittivity have now been sufficiently completely formulated, allowing the permittivity to be rigorously determined with short-range interaction taken into account. In the first case, this involves the use of the Gibbs distribution, and in the second the Kubo formalism. However, although ... the development of equilibrium statistical mechanics may be regarded as complete (from the American foreword to [14]), the reduction of the Gibbs distribution to take into account only the dipole -dipole interactions of nearest-neighbor molecules, as is done in the Kirkwood and Fröhlich theories, cannot be regarded as entirely satisfactory. For such an approach, it is necessary to know the accurate structure of the molecule and the position of the nearest-neighbor molecules, which requires special investigations. In addition, other forms of interaction are omitted, and elastic polarization is not taken rigorously into account.A much more difficult problem confronts theories of nonequilibrium relaxational polarization, in that the development of nonequilibrium statistical mechanics is much worse, since it considers considerably more difficult time-dependent problems and the fundamental question of irreversibility (from the same foreword). In the present review it has been shown that the basic problem of the theory of nonequilibrium relaxational polarization is to find the relation between the macroscopic and molecular distribution functions and to determine the explicit form of these functions. Rigorous solution of this problem for specific materials will allow the laws governing the establishment of relaxational polarization to be determined, together with the corresponding dispersion relations. To this end, in turn, it is necessary to know the relation between the molecular relaxation function and those defects which determine the relaxational process [74].Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 56–73, January, 1979.     

Tunneling migrational polarization in dielectrics

The effect of tunneling accompanying volume-charge relaxation is analyzed. The Fokker-Planck equation, in which tunneling transitions are taken into account in the diffusion coefficient and the mobility in the quasiclassical approximation for rectangular potential barriers, is derived from the condition of transitions of the relaxation oscillators between neighboring states. The distribution of the volume charge was found by solving simultaneously the Fokker-Planck and Poisson equations by the small-parameter method with auxiliary contacts on the electrodes. The region of non-Debye dispersion was determined by taking into account the tunneling of relaxation oscillators. Formulas for calculating the complex dielectric constant were derived.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 71–75, November, 1990.     

Migration polarization in dielectrics and semiconductors

It is shown that during migration polarization the relaxation time is governed by the carrier lifetime in the bound state, by the thickness of the layer through which the migration occurs, and by the drift velocity. An equation is found for ion migration by generalizing the equation for ion-relaxation polarization. Experimental data found by the Ioffe method on the ion mobility in Al₂O₃ are reported and compared with the mobilities obtained by the method of this paper, on the basis of the equation for the relaxation time. Migration polarization must be taken into account in analyzing the mechanism for the excess noise and certain cases of current oscillations in semiconductors, dielectric loss of a relaxation nature, relaxation phenomena in film-type active devices, etc.     

Mechanism of formation of space-charge polarization in dielectrics

A general mechanism of space-charge relaxation in dielectrics, whose separate manifestations were studied in [5–7], is investigated. A strict solution of a system of the nonlinear Fokker-Planck and Poisson equations has been derived in the form of a Fourier series; a recurrent relation is suggested for the oscillation modes which allows the mechanism of space-charge relaxation to be considered as an interaction of modes generated in crystals in an external electric field. Very cumbersome calculations do not allow us to estimate the opportunity of technical applications of the solution obtained within the framework of one paper. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 19–27, November, 2006.     

General multipole expansion of polarization observables in deuteron electrodisintegration

Formal expressions are derived for the multipole expansion of the structure functions of a general polarization observable of exclusive electrodisintegration of the deuteron using a longitudinally polarized beam and/or an oriented target. This allows one to exhibit explicitly the angular dependence of the structure functions by expanding them in terms of the small rotation matrices d ^j _m'm(θ), whose coefficients are given in terms of the electromagnetic multipole matrix elements. Furthermore, explicit expressions for the coefficients of the angular distributions of the differential cross-section including multipoles up to L _max = 3 are listed in tabular form. Received: 19 November 2002 / Accepted: 7 May 2002     

Strong and weak polarization relaxation processes in solid dielectrics

It is established that an increase in the reach-through electrical conductivity of a dielectric can affect the frequency characteristics of the quantity tanδ in different ways when relaxation polarization processes occur: the extrema of the frequency characteristics can be either suppressed or intensified. In the former case, relaxation processes are referred to as weak; in the latter case, they are referred to as strong. Strong processes lead to the emergence of extrema in the frequency dependence of the imaginary part of complex conductivity. The causes underlying the two polarization relaxation processes are identified.     

Contribution of the multipole polarization to the elastic constants in fluorite structure crystals

Numerical calculations are presented for the contribution of the multipole polarization to the elastic constants in fluorite structure crystals. The multipole polarizability is calculated by the self-consistent field treatment of the local density approximation and the spherical solid model. The elastic constants are significantly affected by the multipole polarization of the ions. The contributions of the multipole polarization of the ions to the elastic constant C₁₁, C₁₂, and C₄₄ are about 25%, 40% and 20% of the experimental values, respectively. The calculated values of the deviation from the Cauchy relation are in good agreement with the experimental values.     

Determining the relaxation polarization parameters in dielectrics with high electrical conductivity

In dielectrics with high steady leakage of conductivity, the frequency–temperature dependences of the dielectric loss tangent generally allow us to determine the relaxation time and activation energy of relaxation process only when they are strong. With weak relaxation processes, there are no extrema in the frequency dependence of the dielectric loss tangent. In such cases, the parameters of the relaxation processes are initially determined from the frequency behavior of the imaginary parts of the electrical module or impedance. However, the frequency dependences of these quantities when there is electrical conduction can contain three extrema. Identifying the maxima associated with relaxation polarization therefore requires additional research.     

Linearized gravitation theory in macroscopic media

The refraction of gravitational waves is discussed by developing a macroscopic theory of gravitation along the lines of classical electromagnetism. It is shown that the linearized Bianchi identities may be expressed in a form which is suggestive of Maxwell's equations with magnetic monopoles. The medium is then assumed to be corpuscular in structure and it is shown how, on performing an averaging process on the field quantities, the Bianchi identities must be modified by the inclusion of polarization terms resulting from the induction of quadrupole moments on the individual “molecules”. A model of a medium whose molecules are harmonic oscillators is discussed and constitutive equations are derived. Gravitational waves are demonstrated to slow down in such a medium.     

Spontaneous macroscopic spin polarization in independent spinor Bose-Einstein condensates

We present experimental evidence for the spontaneous formation of a macroscopic spin polarization in overlapping regions of two independent Bose-Einstein condensates produced in different hyperfine states of 87Rb. The condensates are independent in the sense that we do not explicitly introduce a relative phase between them. A single "spin-tip" pulse maps the transverse spin polarization into longitudinal spin polarization, and the atomic density distributions are measured with a Stern-Gerlach imaging method. The resulting matter-wave interference patterns are anticorrelated.     

An analogy between the theory of superfluidity and the theory of dielectrics

It is shown that there is a fruitful correspondence between the properties of dielectrics and the properties of excitations in helium II.     

Mode-coupling theory for the dynamics of tunnelling systems in dielectrics

A mode-coupling theory (MCT) is presented for the spin-boson model with a spectral density which accounts for a heat bath made up of lattice vibrations of a dielectric solid (superohmic dissipation). A usual decoupling approximation provides a set of non-linear integral equations which are solved both numerically by iteration on a computer and analytically by means of a frequency dependent ansatz for the memory functions. There is a transition to incoherent motion at a temperatureT ^* where the bare two-level energy is equal to the damping rate, in contradiction to results obtained previously from a path integral formulation. The discrepancy arises since in the MCT the relevant self-energy function does not exhibit a 1/z-pole atz=0. For tunnelling systems in dielectrics this yields a new relaxation mechanism due to incoherent tunnelling: the present results might require to modify some of the basic assumptions of the standard tunnelling model for dielectric glasses.