Spectral Theory of Perturbative Decays

We propose a complex approach to evaluating afunction sum of two noncommuting non-Hermitianoperators. We propose an explicit expansion of theevolution operator in the case of the neutral K-mesonsystem influenced by an external interaction. Theimportance is pointed out of considering the algebraicexpansion of the time evolution operator whenever thedynamics decouples the internal transitions andcenter-of-mass motion.     

Ferromagnetic resonance in multilayer [Fe/Cr]n structures with noncollinear magnetic ordering

The excitation spectrum in an [Fe/Cr]n multilayer structure with non-collinear magnetic ordering was studied by the ferromagnetic resonance (FMR) method in the frequency interval 9.5–37 GHz at room temperature. Besides an acoustic branch, several additional modes were observed under parallel excitation of resonance. The FMR spectrum was calculated analytically in a biquadratic exchange model, neglecting in-plane anisotropy, for an infinite number of layers in the structure and numerically for a finite number of layers contained in real samples. It was shown that the observed modes correspond to excitation of standing spin waves with wave vectors perpendicular to the film plane. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 9, 690–695 (10 May 1998)     

Anisotropy of optical phonons in semiconductor superlattices: Raman scattering experiments

Experiments on Raman scattering in the “forward” geometry, permitting observation of anisotropy of the optical phonons, are performed on specially prepared short-period GaAs/AlAs superlattice structures with the substrates removed and the surfaces covered with an antireflective layer. The experimental data agree well with the computational results obtained for the angular dispersion of optical phonons in superlattices on the basis of a modified continuum model. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 1, 50–55 (10 July 1998)     

Theory of mixed-polarization propagation in anisotropic cubic media

Polarization dynamics are considered in the presence of an anisotropic Kerr non-linearity in the most common semiconductor waveguide geometry. The equations of motion are formulated in terms of Stokes polarization parameters and their Hamiltonian form is derived. Stationary solutions and their stability are found for plane-wave propagation. It is found that the non-integrable problem of mixed-polarization spatial soliton dynamics can be largely explained in terms of the equivalent plane-wave solutions.     

Field theory of mesoscopic fluctuations in superconductor/normal-metal systems

The thermodynamic and transport properties of normal disordered conductors are strongly influenced by the proximity of a superconductor. A cooperation between mesoscopic coherence and Andreev scattering of particles from the superconductor generates new types of interference phenomena. A field theoretic approach is introduced which is capable of exploring both the averaged properties and mesoscopic fluctuations of superconductor/normal-metal systems. As an example the method is applied to the study of the level statistics of a SNS junction. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 1, 21–26 (10 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Diluted generalized random energy model

A layered random spin model, equivalent to the generalized random energy model (GREM), is introduced. In analogy with diluted spin systems, a diluted GREM (DGREM) is constructed. It can be applied to calculate approximately the thermodynamic properties of spin glass models in low dimensions. For the Edwards-Anderson model it gives the correct critical dimension and 5% accuracy for the ground state energy in two dimensions. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 6, 415–419 (25 March 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

A differential calculus on the quantum groupSU q (2) comparible with the gauge-transformation structure

We consider a three-dimensional bicovariant differential calculus on the quantum group SU_q(2) that is compatible with the structure of gauge transformations. In the approach based on the global covariance with respect to the stability subgroup U(1), we show that the gauge-covariant exterior differential algebra on SU_q(2) is uniquely determined. We construct explicit representations of q-deformed Lie algebras in terms of differential operators. Translated from Teoreticheskaya i Matematicheskaya Fizika, Vol. 116, No. 2, pp. 265–276, August. 1998.     

351 nm, 0.7 ns laser damage thresholds of monomeric liquid-crystalline systems

The 351 nm laser-damage thresholds (at 0.7 nm pulse length) of monomeric liquid crystals are reported and results from aromatic-core samples are compared with those from fully saturated systems. The role of π-electron conjugation is examined and identified as the key cause for laser damage. For UV laser compatibility of devices, the damage behaviour of an alignment-layer polymer (nylon 6/6) was also investigated.     

Structure and defects at Y2BaCuO5 interfaces in melt-textured YBa2Cu3Ox superconductors

Y₂BaCuO₅ (211) inclusions are prominent microstructural features found in melt-textured YBa₂Cu₃O_x (123) superconductors. These particles are of interest because the 123/211 interfaces and the interface-associated defects have been proposed to be flux pinning centers. In addition, the 211 particles are believed to be heterogeneous nucleation centers of dislocation which can increase the critical current density of 123. Unfortunately, only limited studies have been performed on these particles to ascertain their roles in flux pinning. In this investigation, 211 particles, the interfacial structure and defects in undeformed and mechanically deformed melt-textured 123 have been studied by transmission electron microscopy. It was found that there appears to be a preferred orientation between large oblong 211 particles and the 123 matrix. In addition, while the 123/211 interfaces in undeformed 123 are sharp and relatively undistorted, the interfaces in deformed 123 samples are much thicker. Also, the distribution of strained regions and dislocations around oblong 211 particles in undeformed 123 is nonuniform; the interfaces of low surface curvature are relatively free of defects while the surfaces of high curvature are abundant in dislocations. In contrast, the 123/211 interfaces in deformed 123 samples contain high density of dislocations regardless of interface curvature.