Negative Refraction and Subwavelength Lensing in a Polaritonic Crystal

We show that a two-dimensional polaritonic crystal, made of metallic rods that support well defined plasmon oscillations, can act in a narrow frequency range as a medium in which a negative refraction and subwavelength lensing can occur. We show that surface modes are excited on the surface of the lens, and that they facilitate restoration of the evanescent waves, which carry the subwavelength image information. We demonstrate that this can occur in the visible frequency range, for a wide range of materials, including silver and aluminum rods, and carbon nanotubes. This flexibility should allow for an experimental demonstration of this phenomenon in the visible frequency range.Comment: 14 pages; 4 figure

Central mode and soft mode behavior in PbMg1/Nb2/3O3 relaxor ferroelectric

The relaxor ferroelectric PbMg1/Nb2/3O3 was investigated by means of broad-band dielectric and Fourier Transform Infrared (FTIR) transmission spectroscopy in the frequency range from 1 MHz to 15 THz at temperatures between 20 and 900 K using PMN films on infrared transparent sapphire substrates. While thin film relaxors display reduced dielectric permittivity at low frequencies, their high frequency intrinsic or lattice response is shown to be the same as single crystal/ceramic specemins. It was observed that in contrast to the results of inelastic neutron scattering, the optic soft mode was underdamped at all temperatures. On heating, the TO1 soft phonon followed the Cochran law with an extrapolated critical temperature equal to the Burns temperature of 670 K and softened down to 50 cm-1. Above 450 K the soft mode frequency leveled off and slightly increased above the Burns temperature. A central mode, describing the dynamics of polar nanoclusters appeared below the Burns temperature at frequencies near the optic soft mode and dramatically slowed down below 1 MHz on cooling below room temperature. It broadened on cooling, giving rise to frequency independent losses in microwave and lower frequency range below the freezing temperature of 200 K. In addition, a new heavily damped mode appeared in the FTIR spectra below the soft mode frequency at room temperature and below. The origin of this mode as well as the discrepancy between the soft mode damping in neutron and infrared spectra is discussed.Comment: 7 pages with 7 figures, submitted to Phys. Rev.

Improved superlensing in two-dimensional photonic crystals with a basis

We study propagation of light in square and hexagonal two-dimensional photonic crystals. We show, that slabs of these crystals focus light with subwavelength resolution. We propose a systematic way to increase this resolution, at an essentially fixed frequency, by employing a hierarchy of crystals of the same structure, and the same lattice constant, but with an increasingly complex basis.Comment: 16 Pages, 5 Figure

Neutron scattering study of ferroelectric Sn2P2S6 under pressure

Ferroelectric phase transition in the semiconductor Sn2P2S6 single crystal has been studied by means of neutron scattering in the pressure-temperature range adjacent to the anticipated tricritical Lifshitz point (p=0.18GPa, T=296K). The observations reveal a direct ferroelectric-paraelectric phase transition in the whole investigated pressure range (0.18 - 0.6GPa). These results are in a clear disagreement with phase diagrams assumed in numerous earlier works, according to which a hypothetical intermediate incommensurate phase extends over several or even tens of degrees in the 0.5GPa pressure range. Temperature dependence of the anisotropic quasielastic diffuse scattering suggests that polarization fluctuations present above TC are strongly reduced in the ordered phase. Still, the temperature dependence of the (200) Bragg reflection intensity at p=0.18GPa can be remarkably well modeled assuming the order-parameter amplitude growth according to the power law with logarithmic corrections predicted for a uniaxial ferroelectric transition at the tricritical Lifshitz point

Non-linear response of ac conductivity in narrow YBCO film strips at the superconducting transition

Measurements of higher harmonics of the ac voltage response in YBCO thin film strips under low amplitude and low frequency harmonic excitation, as a function of temperature, show a non linear response of the conductivity in the superconducting transition interval. The third and fifth harmonics of the local voltage as a function of T exhibit a peak near Tc and their amplitudes seem to be closely related to the T-derivative of the first harmonic. The peaks are linearly dependent on the current amplitude and do not depend on frequency. The observed data are partially interpreted in terms of ac current induced thermal modulation of the sample temperature added to strong thermally activated fluctuations in the transition region. The fit of the model to the data gives information of some sample properties such as zero temperature critical current, zero onset resistance and thermal boundary conductance

Strong exciton-plasmon coupling in semiconducting carbon nanotubes

We study theoretically the interactions of excitonic states with surface electromagnetic modes of small-diameter (~1 nm) semiconducting single-walled carbon nanotubes. We show that these interactions can result in strong exciton-surface-plasmon coupling. The exciton absorption line shape exhibits Rabi splitting ~0.1 eV as the exciton energy is tuned to the nearest interband surface plasmon resonance of the nanotube. We also show that the quantum confined Stark effect may be used as a tool to control the exciton binding energy and the nanotube band gap in carbon nanotubes in order, e.g., to bring the exciton total energy in resonance with the nearest interband plasmon mode. The exciton-plasmon Rabi splitting we predict here for an individual carbon nanotube is close in its magnitude to that previously reported for hybrid plasmonic nanostructures artificially fabricated of organic semiconductors on metallic films. We expect this effect to open up paths to new tunable optoelectronic device applications of semiconducting carbon nanotubes.Comment: 22 pages, 8 figures, accepted for PR

Effects of multiple abiotic stresses on lipids and sterols profile in barley leaves (Hordeum vulgare L.)

open6siPlants are usually exposed to several types of abiotic stress in regular field conditions. The lipid profile of barley homozygous lines exposed to drought, heat, salinity, and their combinations, was investigated in the present study. Free fatty acids, free sterols, and diacylglycerols were the most abundant classes (∼8.0% of plant material). The genetic background significantly impacted the lipid composition rather than the treatments, and diacylglycerols were the only lipid class affected by salinity (1.84 mg/100 mg plant tissue; ∼33% reduction). However, the genotype × treatment interaction analysis revealed that the lipid and sterol compositions depended on both genotype and environment. Our results suggest that inborn stress tolerance in barley is manifested by enhanced accumulation of most lipids, mainly sterols, especially in heat/drought-stressed plants. In addition, expression of the LTP2 gene may be indirectly involved in the abiotic stress reaction of barley by mediating intracellular transport of some lipid classesopenA. Kuczyńska; V. Cardenia; P. Ogrodowicza; .M. Kempa; M. T. Rodriguez-Estrada; K. MikołajczakaA. Kuczyńska; V. Cardenia; P. Ogrodowicza; .M. Kempa; M. T. Rodriguez-Estrada; K. Mikołajczak

Far-infrared soft mode behavior in PST thin films

Temperature dependences of the optic phonons in $\rm PbSc_{1/2}Ta_{1/2}O_3$ sol-gel films deposited on sapphire substrates were studied by means of Fourier transform far-infrared transmission spectroscopy in the temperature range 20-900\K. Four films displaying different B-site order with both ferroelectric and relaxor behavior were studied. In all cases the TO mode near 80\icm{} at 10\K{} softens on heating to $\approx$45\icm{} following the Cochran law with extrapolated critical temperature near 700\K{} (400\K{} above the temperature of dielectric maximum, $T_{\rm m}$), but above 600\K{} its frequency remains stabilized. It can be assigned to the A$_{1}$ component of the ferroelectric soft mode inside polar clusters which form below the Burns temperature near 700\K. In the ordered PST film another mode activates below T$_{m}$ in infrared spectra near 60\icm exhibiting also anomalous temperature dependence due to its coupling with the former mode. It is assigned to the A$_{1}$ component of the F$_{2g}$ Raman active mode. Central mode, which appears below the Burns temperature in the THz range, is assigned to the dynamics of polar clusters. It slows down on cooling and vanishes from our spectral range below $T_{\rm m}$. Another overdamped excitation assigned to the E component of the soft mode appears near 30\icm{} at low temperatures.Comment: 6 pages, 5 figure

Electron, Muon, and Hadron Lateral Distributions Measured in Air-Showers by the KASCADE Experiment

Measurements of electron, muon, and hadron lateral distributions of extensive air showers as recorded by the KASCADE experiment are presented. The data cover the energy range from about 5x10^14 eV up to almost 10^17 eV and extend from the inner core region to distances of 200 m. The electron and muon distributions are corrected for mutual contaminations by taking into account the detector properties in the experiment. All distributions are well described by NKG-functions. The scale radii describing the electron and hadron data best are approx. 30 m and 10 m, respectively. We discuss the correlation between scale radii and `age' parameter as well as their dependence on shower size, zenith angle, and particle energy threshold.Comment: 28 pages, 14 figures, Accepted for publication in Astroparticle Physic