Gantmakher V.F., Golubkov M.V., Dolgopolov V.T., Shashkin A.A., Tsydynzhapov G.E.. Observation of the parallel-magnetic-field-induced superconductor-insulator transition in thin amorphous InO films // Письма в ЖЭТФ, том 71, вып. 11, http://www.jetpletters.ac.ru

An evidence for phase separation in high-pressure oxygen treated {rm La0.67Ca0.33MnO3/(100)MgO} thin films is presented. This phase separated state is not observed for the x=0.33 classical doping level neither for bulk material, nor for as prepared thin films. It originates from the combined influence of two factors: large strains due to the film-substrate lattice mismatch and high pressure (100 bar) annealing in oxygen. These factors weaken double exchange, drastically enhance low-field magnetoresistance, and lead to hysteresis phenomena. The experimental results are interpreted in terms of phase separation of the film volume into the ferromagnetic conductive matrix with inclusions of spin-glass-like clusters.

We have analyzed about hundred voltage dependent differential resistance dV/dI(V) curves of metallic point contacts between c-axis oriented MgB2 thin film and Ag, which exhibit clear Andreev reflection features connected with the superconducting gap. About one half of the curves show the presence of a second larger gap. The histogram of the double gap distribution reveals distinct maxima at 2.4 and 7~meV, while curves with a single gap features result in more broad maximum at 3.5~meV. The double gap distribution is in qualitative agreement with the distribution of gap values over the Fermi surface calculated by H. J. Choi et al. (cond-mat/0111183). The data unequivocally show the presence of two gaps Delta S=2.45pm 0.15~meV and Delta L=7.0pm 0.45 meV in MgB2 with gap ratio Delta L/Delta S=2.85pm 0.15. Our observations prove further a widely discussed multi-gap scenario for MgB2, when two distinct gaps are seen in the clean limit, while a single averaged gap is present in the dirty one.

The organization of inclusions nucleated in free standing films of smectic-C (SmC) liquid crystal is investigated using polarized light microscopy. Anchoring on the inclusion boundaries induces distortions of the in-plane orientational order of the SmC phase which drive the elastic interactions between inclusions. Such interactions evidence a quadrupolar character. At low concentration, the inclusions self-organize in linear or branched chain structures while at high concentration two-dimensional patterns appear in the film.

The structures formed by inclusions in smectic C (SmC) free-standing films are investigated using polarized light microscopy. The domains confined in these two-dimensional (2D) systems induce distortion of the in-plane orientational order which governs the elastic interaction between the inclusions. The balance between long range quadrupolar attraction and short range repulsion gives rise to a non-trivial collective behaviour of domains. Various 2D structures are created as a function of the concentration and size of the inclusions. We observe the formation of chains and then 2D square lattice when the concentration of domains increases. Further increase of the domain size leads to the transition from square to hexagonal close packed structure.

A theoretical investigation for the conductivity of single walled nanotube films is carried out with an effective medium model in Terahertz region. The results are compared with the recent experiment and a decrease of the real conductivity with increasing frequency is predicted. Meanwhile, the off-diagonal components of the dielectric function of single-walled carbon nanotube films based on the magneto-optical effects are also shown.

The problem of anomalous light tunneling through periodically modulated metal films is examined in a purely analytical approach. The approach uses large magnitude of the dielectric permittivity of metals in the visible and near infrared (it is equivalent to that resulting in the Leontovich boundary conditions for semi-infinite problems). It is shown that the anomalous transparency recently discovered experimentally is caused by the excitation of single- or double-boundary surface plasmon polaritons due to film modulation. Dependencies of the resonance transparency on parameters of the problem are analyzed in detail, and the optimum parameters (optimal layer thickness and optimal modulation amplitude) corresponding to extreme values of the transmittance of both zero and nonzero diffraction orders have been found. Classifying the possible types of the resonances has allowed identifying special and nontrivial features of the effect. In particular, we predict strong nonzeroth-order anomalous transparency.

Anticlinic-synclinic transition was studied in superthin smectic films using polarized light reflected microscopy. The measurements were made in a compound exhibiting the SmCFI1* subphase in a narrow temperature interval between antiferroelectric SmCA* and ferroelectric SmC* phases. In films we observed series of transitions which numbers increases with increasing film thickness. Surface ordering leads to increasing transition temperatures with decreasing film thickness and to change of orientation of the molecular tilt plane in layers. Succession of transitions results from the competition between the surface and the bulk ordering. We found that line string defects may form in film, their orientation and collective behavior result from elastic deformation of molecular ordering.

Light scattering by a small protrusion on a metal surface is analyzed within the framework of perturbation theory. Upon normal incidence of linearly-polarized monochromatic wave, slight deviations of the protrusion shape from a circularly symmetric one lead to formation of optical vortices in the near-field region due resonant excitation of circular surface plasmons. This agrees with the results of scanning near-field optical microscopy experiments revealing distinct spiral patterns in the in-plane near-field intensity distribution for metallized nanostructured polymer substrates.

Using the simple Landau model we discuss near-surface magnetic effects for thin films. corresponding to first-order phase transitions. The size effects observed in ultrathin ferroelectric films are in agreement with this theoretical interpretation. The presence of a weak external field is also formulated.