Effect of Thermionic Emission on Dust-Acoustic Solitons in a Dust-Electron Plasma

The effects of thermionic emission on dust-acoustic solitons with a very small but finite amplitude in a dustelectron plasma are studied using the reductive perturbation technique. The self-consistent variation of dust charge is taken into account. It is shown that the thermionic emission could significantly increase the dust positive charge. The dependences of the phase velocity, amplitude, and width of such solitons on the dust temperature and the dust work function of dust material are plotted and discussed.     

Fermion Bound States Around Skyrmions in Doped Antiferromagnets

We show the skyrmion effects in doped antiferromagnets for the uniform flux phase. The low-energy effective theory of the t‘ - J model can be mapped onto the massive quantum electrodynamics. There exist Fermion bound states around skyrmions. For each sublattice, there exist induced fractional fermion numbers around the skyrmions. The total induced fermion number is zero due to the “cancelling effect“ between two sublattices with Opposite charges.     

Spin-Flip of Polaron in Polymers with a Magnetic Impurity

Using a nonadiabatic evolution method, we investigate the spin-flip process of polaron in polymers with a magnetic impurity. Our results show that when the spin orientation of this impurity is fixed to be perpendicular to the spin of polaron （θ = π/2）, the magnetic impurity causes a spin-flip process. The probability of the spin-flip increases with the increase of exchange integral J up to about 0.35 eV and then decreases with the increase of J. In the case J is fixed while the spin orientation is adjustable, we find the probability of the spin-flip varies with the impurity orientation and reaches a maximum value at θ=π/2.     

Spin Filter Effect in Organic Polymers in the Presence of Local Magnetic Field

Using a nonadiabatic evolution method, we investigate the spin filter effect in organic polymers in the presence of a local magnetic field. Through a spin-dependent magnetic field, polarons （charge carrier） with different spins will feel repulsive or attractive force determined by their spins. Our simulations show that in a single-site magnetic field （affecting electrons at a single site）, for example V150 = 0.35 eV, or V150 = 0.45 eV, a spin-up polaron accelerated to saturated velocity by an electric field can pass through the field while the spin-down polaron is trapped. When the local field extends over several sites （Vn～ exp[-（n - nc）2/nw^2]）, similar behaviour is also found. Simultaneously we find that it is more likely to realize the spin filter effect in a comparatively large field since the polaron which feels attractive force is easily trapped by a local magnetic field.     

Photoinduced Transformation between Charge Carrier and Spin Carrier in Polymers

By dynamical simulations, we show a transforming process between neutral soliton （spin carrier） and charged soliton （charge carrier） in polymers via photo-excitation, taking a polaron as the transitional bridge. It is photoinduced transformation between spin carrier and charge carrier. In this way, we demonstrate an access for polymers to be applied to spintronics.     

Widely Tunable Femtosecond Soliton Pulse Generation by Using Soliton-Frequency Shift in a Photonic Crystal Fibre

Femtosecond Raman soliton generation, tunable from 800 to 1044nm, has been theoretically investigated for a photonic crystal fibre pumped by a 200-fs pulse. A highly nonlinear photonic crystal fibre with a length of only 57.7cm and a nonlinear coefficient of 0.075 (Wm)^-1 is used to achieved such a broadband. It is found that the spectral bandwidth increases with the input peak power. In particular, it is also found that the output wavelengths of the resulting sub-40 fs Raman solitons can also be tuned effectively by varying the initial pulse chirp. There exists an optimal positive chirp which maximizes the bandwidth, corresponding to the formation of only one long-wavelength Raman soliton.     

Breathing Bright Solitons in a Bose—Einstein Condensate

A Bose-Einstein condensate with time varying scattering length in time-dependent harmonic trap is analytically investigated and soliton-like solutions of the Gross-Pitaeviskii equation are obtained to describe single soliton, bisoliton and N-soliton properties of the matter wave. The influences of the geometrical property and modulate frequency of trapping potential on soliton behaviour are discussed. When the trap potential has a very sinall trap aspect ratio or oscillates with a high frequency, the matter wave preserves its shape nearly like a soliton train in propagation, while the breathing behaviour, which displays the periodic collapse and revival of the matter wave, is found for a relatively large aspect ratio or slow varying potential. Meanwhile mass centre of the matter wave translates and/or oscillates for different trap aspect ratio and trap frequencies.     

Soliton Solutions and Interaction Between a Line Soliton and a y-Periodic Soliton in Generalized （2W1）-Dimensional Nizhnik-Novikov-Veselov Equation

Using the variable separation approach, many types of exact solutions of the generalized (2 1)-dimensional Nizhnik-Novikov-Veselov equation are derived. One of the exact solutions of this model is analyzed to study the interaction between a line soliton and a y-periodic soliton.     

Phase Shifts during Interaction between Two Solitons in Two-Dimensional Dusty Plasma

The dust acoustic solitary waves propagating in two different directions in two-dimensional dusty plasma are investigated. In order to study the soliton interactions in multi-dimensional systems, we extend the reductive perturbation method and obtain two Kortewe-de Vries equations for nonlinear waves in both the ξ and 77 directions, respectively. The phase shifts after collision of two solitons with arbitrary angle are given. Finally, the solution of na up to O（ε^4） order is obtained.     

Dynamical Stability of Gap Soliton of One-Dimensional Condensate in Optical Lattices with Strong Interatomic Interaction

By developing the multiple scales method, we analytically study the dynamics properties of gap soliton of Bose- Einstein condensate in optical lattices. It is shown that the gap soliton will appear at Brillouin zone edge of linear band spectrum of the condensates when the interatomic interaction strength is larger than the lattice depth. Moreover, the density of gap soliton starts to be relatively small, while it increases with time and becomes stable.     

Effect of Temperature on Polaron Stability in a One-Dimensional Organic Lattice

Effect of temperature on the polaron stability in a one-dimensional organic lattice is investigated within the Su-Schrieffer-Heeger model. The temperature effect is simulated by introducing random forces to the equation of the lattice motion. It is found that the localized polaron state becomes delocalized even at low temperatures. The time of polaron keeping localized depends on the magnitude of temperatures. By taking into account the thermal effect, we find that the dissociation field is weaker as compared with earlier works.     

Theory of gel point in real polymer solutions

We develop a new theory of gelation which takes into account (i) delay of the gel point and (ii) change of functionality due to ring formation. We show that the problem of finding the gel point in real polymer solutions reduces to the problem of calculating the total ring concentration and the extent of reaction of intermolecular reaction at the gel point. In this paper, we solve a special case of this problem, on the basis of the independence assumption between intermolecular reaction and cyclization which takes into account only (i) the delay of the gel point: making use of the asymptotic equality of the total ring concentration, we acquire an approximate solution for the gel point D_c as a function of the inverse concentration , the relative frequency of cyclization and dimension d. Applying the observed values of in linear polyesters, the theoretical result reproduces well the Wile and the Gordon-Scantlebury observations, showing the existence of a critical dilution beyond which gelation can not occur, and an asymptote . As the classical gel point is approached, the present theory reduces to the linear equation, which makes one-to-one correspondence with the real slope , suggesting the inequality which is just what polymer chemists have quested for so far, with the physical meaning having remained unknown. Receveid: 30 December 1997 / Revised: 28 May 1998 / Accepted: 12 June 1998     

Infrared reflectivity of Cox(SiO2)1−x (x∼0.85, 0.55, 0.38) granular films on SiO2 glass substrates

We report the infrared specular reflectivity of Co_x(SiO₂)_1−x (x∼0.85, 0.55, 0.38) films on SiO₂ glass spanning from a metal-like to insulating behavior. While films for x∼0.85 show carrier metallic shielding and hopping conductivity, for x∼0.65 and lower concentrations, the nanoparticles’ number and size promote a localization edge near the highest longitudinal optical frequency. Such an edge is associated with a reflectivity minimum and a higher frequency band connoting strong electron-phonon interactions, carrier phonon assisted hopping, and polaron formation. Optical conductivity fits with current polaron models provide grounds toward a microscopic understanding of transport properties in these as-prepared granular films.     

Experimental and theoretical studies of polaron optical properties in KNbO3 perovskite

Time-resolved absorption and luminescence spectra have been measured in KNbO₃ perovskite crystals after pulsed band-gap excitation by 200 fs laser pulses and 10 ns electron pulses. Quantum chemical calculations using the large unit cell periodic model support the interpretation of the observed transient absorption bands at 0.8 and 1.1 eV as the self-trapped electron polarons and bound hole polarons, respectively. The activation energy for the 2.2 eV green luminescence quenching is 0.05 eV. We suggest that the short lifetime (<15 ns) of the luminescence at RT is caused by the radiative recombination of nearest electron and hole polarons.     

Ground State of a Polaron in a Symmetric Triangular Quantum Well

We study the effects of electron-phonon interaction on the electron ground state in a symmetric triangular quantum well, and calculate the ground state energy of an electron in the GaAs/Al0.96Ga0.04As triangular quantum well including the effects of the interaction between electrons and confined LO phonons by using a modified Lee-Low-Pines variational method. The electron wavefunction in the triangular well is chosen as the Airy function. The numerical results are given and discussed.     

Spin injection in an organic device with a spin polarized self-assembled monolayer

We propose to achieve spin injection in an organic device by a spin polarized self-assembled monolayer (SPSAM), which is used to tune the spin-dependent coupling between electrode and organic polymer. The results show that spin injection can be realized by both the spin selection and spin manipulation effects of the SPSAM. Interestingly, we found spin polarized wave-packet as a consequence of the spin injection, which is a mix of a normal spin polaron and a spinless bipolaron.     

Dynamic process of self-trapped polaron in photoexcited SrTiO3

Relaxation process of self-trapped polaron is investigated by a nonadiabatic molecular dynamic method. We show localized disorder due to lattice fluctuations can give rise to a tightly-bound electronic state in ultraviolet illuminated SrTiO₃ crystal. This bound state is actually a self-trapped polaron in accordance with the experimentally observed large Stokes-shift. The formation of the self-trapped polaron is shown to be an ultrafast process.     

Electron-phonon effects on Stark shifts of excitons in parabolic quantum wells: Fractional-dimension variational approach

Electron-phonon effects on Stark shifts of excitons in parabolic quantum wells are studied theoretically by using a fractional dimension method in combination with a Lee-Low-Pines-like transformation and a perturbation theory. The numerical results for the exciton binding energies and electron-phonon contributions to the binding energies as functions of the well width and the electric field in the Al_0.3Ga_0.7As parabolic quantum well structure are obtained. It is shown that both exciton binding energy and electron-phonon contributions have a maximum with increasing the well width. The binding energy and electron-phonon contribution decrease significantly with increasing the electric-field strength, in special in the wide-well case.