Structure of π- and 2π-Walls in Smectic films

The structure of ??- and 2??-walls in smectic films was reconstructed from optical reflectivity measurements. Investigations were made in free standing films of nonpolar Smectic-C and ferroelectric Smectic-C* liquid crystals. ??-walls are observed in magnetic field and 2??-walls in electric field parallel to the film plane. For the first time the distribution of molecular orientation across the walls was determined. Peculiarities of the wall structure related to the anisotropy of the film elasticity were found. The structure of the walls is well described by the theory taking into account the anisotropy of two-dimensional elasticity of smectic films.     

Observation and theory of strong stripe domains in amorphous sputtered FeB films

Domain structures in thin sputtered amorphous FeB films are studied by means of the longitudinal Kerr effect. In addition to the irregular domain structure characteristic of soft magnetic materials, we observe in certain regions a fine equilibrium domain structure with periodicity of a few micrometers. The Kerr contrast indicates that the magnetization at the surface of the film lies partially along the stripe direction. These characteristics and the behavior in applied fields suggests that the domains are similar to type II “strong stripe domains” observed earlier in permalloy films. Extending an earlier theory by Hara, we use a stray-field-free model with tilted orthorhombic anisotropy to show that there are at least two qualitatively different strong stripe structures: type IIa with surface magnetization perpendicular to the stripes and type IIb with surface magnetization at least partially parallel to the stripes. Type IIb is favored when K_p/K₀<cos 2θ ₀ where K₀ is the anisotropy component with axis tilted by θ₀ out of the film plane, and K_p is an in-plane anisotropy perpendicular to K₀. Strong stripes in amorphous FeB appear to be type IIb while those in permalloy are usually type IIa.     

Thickness dependent stripe structure stability of Ag films on Si(1 1 1)-(4 × 1)-In substrate

The thickness dependent stripe structure stabilization of Ag films on Si(1 1 1)-(4 × 1)-In substrate is thermodynamically considered. It is found that for the stability of the structure, there is a competition between the sum of elastic energy and stacking fault energy in the film and the film-substrate interface energy. The presence of equilibrium of them leads to a critical film thickness. Beyond it, the stripe structure will transform into a flat one. Our prediction for n_c of Ag films shows reasonable agreement with experimental data. In addition, according to the established model, it is predicted that Au could also form the above stripe structure on this substrate with a similar n_c value of Ag.     

Estimating of CP-violation in <Emphasis Type="Italic">B</Emphasis><Superscript>0</Superscript>→ψ(2<Emphasis Type="Italic">S</Emphasis>)π<Superscript>0</Superscript> decay

I present estimates of CP-violating asymmetries in the non-leptonic charmonium two-body B⁰→ψ(2S)π⁰ decay and the same decays of B⁺→ψ(2S)π⁺ and B⁺→ψ(2S)K⁺ These estimates are based on QCD and improved QCD factorization approach making use of next-to-leading order (NLO) contributions. The CP-violating asymmetry for B⁰→ψ(2S)π⁰ decay is not available, according to the same calculations, it is expected if it can be measured in the future its value will be S_ψ(2S)π0(B⁰ → ψ(2S)π⁰)= 0.662 ± 0.197 and C_ψ(2S)π0(B⁰ → ψ(2S)π⁰)= 0.024 ± 0.007.     

Vortex lattice matching effects in a washboard pinning potential induced by Co nanostripe arrays

An advanced mask-less nanofabrication technique, focused electron beam-induced deposition (FEBID), has been employed on epitaxial Nb thin films to prepare ferromagnetic decorations in the form of an array of Co stripes. These substantially modify the non-patterned films’ superconducting properties, providing a washboard-like pinning potential landscape for the vortex motion. At small magnetic fields B ? 0.1 T, vortex lattice matching effects have been investigated by magneto-transport measurements. Step-like drops in the field dependencies of the films resistivity ρ(B) have been observed in particular for the vortex motion perpendicular to the Co stripes. The field values, corresponding to the middle points of these drops in ρ(B), meet the vortex lattice parameter matching the pinning structure’s period. These disagree with the results of Jaque et al. (2002) [11], who observed matching effects corresponding to the stripe width in Nb films grown on periodically distributed submicrometric lines of Ni.     

A determination of the forward K±p B amplitude and the hyperon coupling constants

From the K^±p forward B amplitude a new amplitude is constructed in such a way that its imaginary part can be calculated from the K^±p polarization data. A prediction of the B amplitude is obtained and the hyperon coupling constants are determined with the result (G_NΛK²+0.8G_NΣK²)/4π = 12.2 ± 2.5.     

Length scale dependence of chiral symmetry breaking in free-standing films of achiral smectic C

The textures of a smectic C phase in free-standing films of the Schiff base 5O.6 are studied as a function of the number of layers and temperature. Periodic stripes with alternating contrast are observed in SmA boundary layers. On further cooling a transition to the splay stripes occurs in the smectic A temperature interval. In the smectic C phase all the periodic textures disappear, whereas in films with one free boundary a periodic arrangement of splay stripes is found. Mechanisms of symmetry breaking are discussed. Pis'ma Zh. éksp. Teor. Fiz. 64, No. 1, 29–32 (10 July 1996) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Spin−wave resonance as a way of studying the constant of surface anisotropy,using films of Fe–Ni alloy as an example

The effect the thickness and concentration composition of a ferromagnetic thin film have on surface anisotropy constant K _S is investigated. Spin–wave resonance is chosen as a way of detecting and measuring the K _S value. Fe–Ni thin films are synthesized via chemical deposition. Dependences of K _S on the content of Ni in the alloy and a film’s thickness are established.     

Measurement of the KS0 → π+π−γ decay rate

From a study of 70 000 K° decays in the CERN 2m hydrogen bubble chamber, we have estimated the rate for K_S⁰ → π⁺π^?γ for different cuts in the γ momentum. The results are in good agreement with inner bremsstrahlung on K_S⁰ → π⁺π^?. For γ momentum in the K° c.m. greater than 50 MeV/c, we obtain the branching ratio: Γ(K_S → π⁺π^?γ, k>50 MeV/c)/Γ(K_S→π⁺π^?)=(2.8. ± 0.6)×10^?3. This leads to an estimate for the direct γ emission process: Γ(K_S→π⁺π^?γ direct)/Γ(K_S → π⁺π^?)=(0.3 ± 0.6) × 10^?3.     

Theoretical description of fluctuations in free-standing smectic-A films including spatial non-uniformity of their elastic characteristics

A theoretical study is reported of fluctuations in smectic layer displacements and of the correlations between them in free-standing smectic-A films formed of liquid-crystal compounds with smectic-A-isotropic liquid (Sm-A-I) and Sm-A-nematic (Sm-A-N) bulk phase transitions. The study took into account the dependence of the elastic constants for bending, K, and tension (compression), B, of smectic layers on distance to the free film surfaces. The calculations are compared with the results obtained within Hołyst’s model for spatially uniform, free-standing smectic-A films. It has been established that, below the temperature at which smectic order in the bulk of a liquid crystal disappears, taking into account the profiles of the elastic moduli K and B does not produce noticeable differences from this model. However, at temperatures considerably above the Sm-A-I and Sm-A-N phase transitions, their inclusion results in considerable discrepancies from the predictions of Hołyst’s model. Fiz. Tverd. Tela (St. Petersburg) 41, 1882–1889 (October 1999)     

Optical measurement of KB/KS divergence in nematics

A direct optical analysis of the divergence of the elastic constant ratio K_B/K_S in a nematic material near the T_AN transition temperature is presented. The results are in excellent agreement with what obtained from more complicated techniques. The method used exhibits a large number of advantage with respect to the conventional ones.     

Observation of KS0 semileptonic decays with the CMD-2 detector

The decay K_S⁰→πeν has been observed by the CMD-2 detector at the e⁺e⁻ collider VEPP-2M at Novosibirsk. Of 6 million produced K_L⁰K_S⁰ pairs, 75±13 events of the K_S⁰→πeν decay were selected. The corresponding branching ratio is B(K_S⁰→πeν)=(7.2±1.4)×10⁻⁴. This result is consistent with the evaluation of B(K_S⁰→πeν) from the K_L⁰ semileptonic rate and K_S⁰ lifetime assuming ΔS=ΔQ .     

Dense stripe domains in a nanocrystalline CoFeSiB thin film

We recently reported a possible antiferromagnetically coupled phase in a Co-rich CoFeSiB thin film, that had a partially nanocrystalline Co phase in an amorphous CoFeSiB matrix. Although an amorphous CoFeSiB film should show a ferromagnetic behavior, we observed an antiferromagnetic coupling associated with a nanocrystalline Co phase in the hysteresis-loop measurements of Co-rich CoFeSiB thin films. We ascribed the observed antiferromagnetic coupling to dense stripe domains consisting of periodically up and down domains perpendicular to the surface of the film. The configuration of the stripe domains was confirmed with magnetic force microscopy images. When a longitudinal magnetic field was applied, the size of the stripe domain was reduced. While for a transverse field, the domain structure became tilted and zigzagged, but no in-plane magnetic anisotropy was noted. When the magnetic field was increased to values above the saturation magnetic field, H_S = 2.5 kOe, the domain structure disappeared.     

Low energy constraints on N = 2 supersymmetric models

We derive constraints on the masses of mirror particles in N = 2 supersymmetric theories. We consider the K_L?K_S mass difference, the π → ev/π → μv branching ratio and the anomalous magnetic moment of the muon. The K_L?K_S mass difference gives a lower bound of 15 TeV on the mirror gauge scalar and mirror gauge fermion masses, under suitable assumptions.     

Spontaneous S_ gratings and specific features of their formation and evolution in photosensitive AgCl-Ag films

The formation and evolution of spontaneous S_ gratings in photosensitive waveguide AgCl-Ag films under the action of a laser beam are investigated experimentally and theoretically. It is found that in the cases of s and p polarizations of laser radiation these gratings differ significantly not only in the period but also in the structure and spatial and temporal stability. The different character of the gratings is explained in detail by the competition between the S_ gratings and other gratings evolving simultaneously in the film and the change in the scattering indicatrix in the case of p polarization as a result of intense evolution of degenerate C gratings. The regularity of S_ gratings on TM₀ modes in the case of p polarization and large angles of incidence makes it possible to increase the accuracy of determining the refractive indices of substrates using AgCl films corresponding to the cutoff thicknesses of TM₀ waveguide modes.     

Search for CP-violation in Ko→3πo decay

Using the 180 liter ITEP liquid xenon bubble chamber the time distribution of 22 K^o → 3π^o decays has been studied. For the ratio η_ooo of amplitudes K_S → 3π^o and K_L → 3π^o decays we found Reη_ooo = ?0.04 ± 0.45 and Imη_ooo = 0.45 ± _0.65^0.50. Assuming CPT invariance we obtained |η_ooo|² < 1.2 and Γ(K_S → 3π^o)/ Γ(K_S) ? 4.3 × 10^?4 at 90% confidence level.     

Phase transition to anticlinic texture in free-standing smectic c films

Experimental data on the optical reflectance of free-standing smectic C films were analyzed within the framework of a phenomenological Landau approach. At a certain temperature T _0N (determined from experimental data), which exceeds the known temperature T _c of the volume phase transition from smectic A to smectic C state, a surface phase transition takes place whereby molecules in the surface layer become sloped relative to the normal of the smectic layers. The transition temperatures T _0N ^s,a for N-layer films possessing synclinic (symmetric) and anticlinic (antisymmetric) textures of the order parameter (tilt angle θ) were determined. A comparison of the theoretical and experimental data allowed all parameters of the model to be determined (including critical indices of the correlation length and the surface order parameter). Three possible models of the transition from the state with transverse polarization (perpendicular to the molecular tilt plane) to the state with longitudinal polarization (parallel to this plane) are analyzed. The transition takes place at low (°–°) values of the order parameter θ in the middle layer of the film.     

High-frequency excitations of stripe-domain lattices in magnetic garnet films

Magnetic garnet films of composition (Y,Bi)₃(Fe,Al)₅O₁₂ have been grown by liquid phase epitaxy on [111] and [110] oriented substrates of gadolinium gallium garnet. The domain wall resonance and the two branches of the domain resonance of periodic stripe domains are measured as function of the bias induction applied in the film plane parallel to the stripes. Resonance frequencies up to 7.5 GHz are observed. An improved version of the hybridization model is developed to describe these resonances. It turns out that hybridization of the domain resonance branches is determined by the cubic anisotropy for [111] oriented films, while for [110] oriented films coupling of the domain resonances is mainly caused by the orthorhombic anisotropy. The theoretical model is in excellent agreement with experiments, no fitting parameters are used. It is also used to derive the phase relation between the precessing magnetizations of neighbouring domains.     

Critical currents of LaMo6S8 thin films

The thin films of LaMo₆S₈ were prepared by d.c. getter sputtering method. Critical current have been measured vs applied magnetic field B_⊥ up to 8 T at the temperature ranged from 1.7 to 4.2 K. The highest critical current density reached was J_c = 1.7 × 10⁷ Am^?2 at B = 0 and T = 1.7 K. Based on the measurements performed, it was possible to indicate that depending on the heat treatment applied, the pinning forces created in the LaMo₆S₈ thin films obey the scaling law.     

Stripe instability in thin films of smectic liquid-crystal polymers

Two-dimensional nanostripes are formed in thin films of side-chain liquid-crystalline polymer films when the material enters the smectic phase. The structure is investigated using transmission electron microscopy. Electron diffraction patterns show that the chain molecules are mostly aligned in the film plane and the average molecular director is parallel to the direction of the stripes. We discuss factors affecting the stripe amplitude and periodicity, such as the film thickness and the temperature of annealing in the nematic phase, and suggest a possible mechanism for their formation. We propose that an equilibrium instability occurs due to a competition between the layer-aligning effect of the substrate and the planar director alignment, forcing smectic layers perpendicular to the film surface. The stripes decorate the overall patterns of nematic director in the polymer film and provide a means of high-resolution imaging for observation of textures and disclinations.Received: 10 June 2003, Published online: 19 August 2003PACS: 68.37.Lp Transmission electron microscopy (TEM) (including STEM, HRTEM, etc.) - 61.30.Vx Polymer liquid crystals - 61.30.Hn Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions - 68.55.Nq Composition and phase identification