Analysis of the orientational effects on infrared absorption spectra in p-type semiconductor quantum wells

We theoretically investigate the effects of layer orientation on valence subband optical absorption in cubic semiconductors. We analyze the polarization dependence of matrix elements for hole subband transitions at zero in-plane momentum, and make predictions concerning infrared absorption spectrum. The role of orientation as a key parameter in valence subband spectroscopy is clarified. The absorption spectra for 011 layer orientation is calculated, demonstrating the in-plane optical anisotropy.     

Optical Theorem in Quantum electrodynamics with Unstable Vacuum

All the results reffering to the relations of the optical theorem in QED with an external electromagnetic field with unstable vacuum are consistently given in this paper. The results obtained are true in all orders of perturbation theory. A generating functional is introduced for calculating total probabilities of any processes in QED with unstable vacuum.     

A geometrical approach to theK-divisibility problem

We give a geometrical interpretation of the Brudnyi-KrugljakK-divisibility theorem—one of the fundamental results of modern interpolation theory of Banach spaces. We show that this result is closely connected with a curious intersection theorem which can be formulated in the spirit of Helly’s classical theorem. LetB ₀,B ₁ be two closed convex balanced subset of a Banach spaceX. We prove that under a wide range of various conditions the family of setsB = {B =sB ₀ +tB ₁ +c;s, t ∈R,c ∈X} possesses the following intersection property: LetB′ be a subfamily ofB such that every two sets fromB′ have a common point. Then ∩ _B∈B′ γ oB ≠ 0, where γ>0 is an absolute constant (γ ≤ 7 + 4 √2) and the symbol γ oB denotes a dilation ofB with respect to its center by a factor of γ. As a consequence we obtain a generalization of theK-divisibility theorem for sums of two elements. Supported by the Center for Absorption in Science, Israel Ministry of Immigrant Absorption and by grant No. 95-00225 from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel.     

Hyperbolic Chevalley groups on ℂ<Superscript>2</Superscript>

Let Γ ? U (1, 1) be the subgroup generated by the complex reflections. Suppose that Γ acts discretely on the domain K = {(z ₁, z ₂) ∈ ?² ||z ₁|² ? |z ₂|² < 0} and that the projective group PΓ acts on the unit disk B = {|z ₁/z ₂| < 1} as a Fuchsian group of signature (n ₁, ..., n _s ), s ? 3, n _i ? 2. For such groups, we prove a Chevalley type theorem, i.e., find a necessary and sufficient condition for the quotient space K/Γ to be isomorphic to ?² ? {0}.     

Crossover from ferroelectric to relaxor behavior in BaTi1− x Sn x O3 solid solutions

Dielectric relaxation of BaTi_{1? x} Sn _x O₃ ceramics is investigated by means of dielectric spectroscopy. The gradual crossover from ferroelectric to relaxor behavior is characterized by vanishing of the contribution due to domain walls and appearance of relaxation related to reorientation of polar nanosized regions. Typical behavior of relaxors is observed only in ceramics with x = 0.30, while the compositions with 0.175 ≤ x ≤ 0.25 show coexistence of both ferroelectric and relaxor features. The relaxor properties are supposed to be due to both weak random fields and disorder inherent in pure BaTiO₃.     

Two-dimensional Ising model criticality in a three-dimensional uniaxial relaxor ferroelectric with frozen polar nanoregions

The charge-disordered three-dimensional uniaxial relaxor ferroelectric Sr0.61Ba0.39Nb2O6 splits up into metastable polar nanoregions and paraelectric interfaces upon cooling from above Tc. The frozen polar nanoregions are verified by piezoresponse force microscopy, respond domainlike to dynamic light scattering and dielectric excitation, reveal nonergodicity at T>Tc via global aging, and coalesce into polar nanodomains below Tc. Contrastingly, the percolating system of unperturbed interfaces becomes ferroelectric with two-dimensional Ising-model-like critical exponents alpha=0, beta=1/8, and gamma=7/4, as corroborated by ac calorimetry, second harmonic generation, and susceptometry, respectively.     

Electron in a quantized plane-wave field and in the classical field of a longitudinal electric wave

The Dirac equation is solved for an electron moving in a quantized plane-wave field in the classical field of a longitudinal traveling electric wave propagating in one direction. Through a canonical transformation of the photon creation and annihilation operators the problem is reduced to a quasiparticle problem; the quasiparticle energy depends on the time and the coordinates.     

Green's function for a system consisting of a charged particle and a quantized plane wave

An integral representation in terms of the intrinsic time is obtained for Green's function of a system consisting of a charged spinless particle intersecting with the field of a quantized plane wave.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 54–58, August, 1978.