Nonlinear Dynamic Phenomena in Macroscopic Tunneling

Numerical simulations of the NLSE (or GPE) are presented demonstrating emission of short pulses of the matter (light) density formed in the course of tunneling in wave-guided light and/or trapped BEC. The phenomenon is observed under various conditions, for nonlinearities of different signs, zero nonlinearity included. We study, both numerically and analytically, pulsations of matter (light) remaining within the trap and use the results in order to induce emission of sequential pulses by properly narrowing the trap. This allows us to propose a mechanism for a realization of Atom Pulse Laser.Comment: 14 pages, 6 figure

Variation of the energy gap of the SbSI crystals at ferroelectric phase transition

Variation of the forbidden gap of SbSI crystals in the phase transition region is analyzed on the pseudopotential method for antiferroelectric and ferroelectric phase. The band gap at several special points of the Brillouin zone and some characteristic parameters of the band are considered. During the phase transition, the most significant changes are observed with the valence band top at points Q, C, R, H, E and with the conduction band bottom at points H, T and E of the Brillouin zone. At the ferroelectric phase transition, the valence and conduction bands change due to displacement of Sb and S atoms with respect to I and with respect to each other as a result of order–disorder and displacement-type transition. The obtained band gap values agree quite well with the experiment. This is apparently due to application of neutral rather than ionic atomic functions and inclusion of sufficiently many plane waves in the basis set for calculationVytauto Didžiojo universitetasŠvietimo akademij

Investigation of the vibration spectrum of SbSI crystals in harmonic and in anharmonic approximations

The force constants of SbSI crystal have been calculated by the pseudo-potential method. The frequencies and normal coordinates of SbSI vibration modes along the c(z) direction have been determined in harmonic approximation. The potential energies of SbSI normal modes dependence on normal coordinates along the c(z) direction V(z) have been determined in anharmonic approximation, taking into account the interaction between the phonons. It has been found, that in the range of 30–120 cm−1, the vibrational spectrum is determined by a V(z) double-well normal mode, but in the range of 120–350 cm−1, it is determined by a V(z) single-well normal modeVytauto Didžiojo universitetasŠvietimo akademij