Effect of interdiffusion on electronic states in one-layer quantum ring superlattice

The effect of interdiffusion on band structure and Bloch amplitudes of two dimensional superlattice composed of initially cylindrical quantum rings is investigated in the framework of adiabatic approach and using transformation to in-plane momentum space. It is shown that the adiabatic approximation is applicable even if the ring’s height is equal to its radius, because of weak localization of electron in the superlattice plane comparing with the localization in perpendicular direction. The consideration of the dependence of effective mass on spatial coordinate and time leads to the energy correction up to 10 meV. It is shown that energy minibands rise and become wider due to interdiffusion and the dependence of Bloch amplitudes on quasimomentum direction is more pronounced in the case of diffused potential profile.     

Solitons in a ferrimagnet

Exact N-soliton solutions of nonlinear Landau-Lifschitz equations are obtained by means of the modified form of the inverse scattering method (“dressing method”) for the case of an isotropic ferrimagnet with two non-equivalent sublattices.     

Mixed state in a superlattice

Presented in this paper is a theoretical calculation of the vortex solution in a chosen superlattice (Nb/NbZr) using the Gibbs free energy of an inhomogeneous superconductor. The eigenvalue obtained in this geometry from de Gennes-Werthamer proximity coupling theory is first examined according to a set of experimental data, while the correspondent eigenfunctions are then used to construct vortex solutions with either square lattice or triangle lattice symmetry. The Gibbs free energy is calculated in terms of the vortex solutions of both symmetries. The effective Ginzburg-Landau parameter,K _NS , for this superlattice is determined asK _NS =0.218 by requiring a consistency between the microscopic and macroscopic theoretical calculations. Of particular importance is a new mechanism revealed by this calculation that a highly localized state of superconducting condensate in its hosting layer, despite the spatially rapid varying characteristic of its correspondent nucleating order parameter, provides a lower eigenvalue state, which results in a dimensional crossover. A further examination of this mechanism is carried out in the mixed state calculation. Finally, a generalization of the present theoretical results to a large class of superlatices is discussed.     

Solitons in a two-dimensional electron gas

The non-linear spectrum of a two-dimensional electron gas (2-DEG) formed at the interface of a heterostructure is investigated. This spectrum is found to contain a new type of localized excitation exhibiting soliton behavior. A matrix formulation of the model equations permits the extraction of the equation of evolution in space for these excitations. Results are presented for the boundary value problem excited by temporal Gaussian pulses.     

Plasmons in a planar graphene superlattice

Plasmon collective excitations are studied in a planar graphene superlattice formed by periodically alternating regions of gapless graphene and of its gapped modification. The plasmon dispersion law is determined both for the quasi-one-dimensional case (the Fermi level is located within the minigap) and for the quasi-two-dimensional case (the Fermi level is located within the miniband). The problem concerning the absorption of modulated electromagnetic radiation at the excitation of plasmons is also considered.     

Effect of interdiffusion on electronic states of strain-free Gaussian-shaped double quantum ring superlattice

The effect of interdiffusion on band structure and Bloch amplitudes of three dimensional superlattice composed of Gaussian shaped double quantum rings is investigated using the Fourier transformation to the momentum space. It is shown that the sequence of the principal quasimomentum vectors which correspond to the energy increase depends on superlattice symmetry. Due to interdiffusion both the first and the second minibands of conduction band shift to the region of higher energies and broaden, meanwhile the difference between the behaviors of the dispersion curves in different directions of momentum space gradually disappears. The obtained results indicate to the opportunity of purposeful manipulation of structure characteristics by means of interdiffusion both quantitively and qualitatively.     

Piezoelectric-induced polariton coupling in a superlattice

Propagation of electromagnetic waves in a piezoelectric superlattice is studied. Because of the piezoelectric effect, a coupling between two orthogonally polarized electromagnetic waves is induced by the superlattice vibration. As a consequence of the strong coupling, two types of polariton modes are found: one is supported in the band gap while the other prohibited. This unusual coupling effect is not present in classical lattices.     

Magnetic susceptibility in a layered superlattice

Paramagnetic and diamagnetic contributions to the magnetic susceptibility are calculated for a layered superlattice as a function of the temperature in both degenerate and nondegenerate regimes. The susceptibility shows distinctly different temperature dependences as the inter-layer bandwidth as well as the Fermi energy is varied from a two-dimensional to a three-dimensional regime, thus giving valuable information about the electron density and the inter-layer tunneling.     

Vertical charge transport in a superlattice

It is demonstrated that the vertical charge transport in a superlattice is influenced uniquely by the difference in the effective mass of the electron between its adjacent layers. The mass difference produces a coupling between the parallel and vertical motions of the electron. As a consequence, the vertical velocity of an electron depends not only on its wavevector in the vertical direction but also on the wavevector in the direction parallel to the layers. As an illustration of the effect, a qualitative analysis is made to show that the vertical motion of the electron wavepacket can be altered by the application of a magnetic field whose direction is normal to the layers.     

Electron Polarization Solitons in a Helical Molecule

Journal of Experimental and Theoretical Physics - The evolution of the spin of an electron moving along the axis of a long helical molecule under the action of an external field is investigated....     

Solitons in a disordered anisotropic optical medium

The radiation-mediated interaction of solitons in a one-dimensional nonlinear medium (optical fiber) with birefringent disorder is shown to be independent of the separation between solitons. The effect produces a potentially dangerous contribution to the signal lost.     

Envelope Solitons in a Plasma-Slab Condenser System

It is the purpose of this work to study the propagation of nonlinear wave packets in a plasma-slab condenser system, which can be described as a nonlinear dispersive transmission line.     

Solitons in a linear lattice with defects

Solitons are generated in an anharmonic linear lattice in which neighbouring atoms interact through a Morse potential by giving either a strong initial impulse or a large displacement to an end atom. Studies on the variation of the characteristic properties of the soliton with the strength of the initial pulse show that the velocity and the amplitude of the soliton increase with the strength of the initial impulse, but below a certain critical value for the initial impulse, only an oscillatory tail is generated. It is shown that when a defect is present in the lattice, a localised mode appears at the site of the defect and additional solitons travelling forward or even backwards, are generated. When two solitons collide at a defect region, they reemerge but leave a localised mode at the site of the defect. If an initial velocity is imparted to a particular particle, synchronously with the crossing of the particle by the soliton, a localised mode emerges at the site of the particle and additional solitons are also generated. When a soliton moves from a denser to a rarer medium, a strong localised pulse is created near the region of the density discontinuity and additional solitons appear; and further a weak oscillatory tail is left behind in the denser medium. On the other hand, if a soliton moves from a rarer to a denser medium, it is reflected back and a small localised mode is generated at the site of the density discontinuity. The variation of amplitude of the soliton with the velocity of propagation is also studied.     

Solitons in a magnetized relativistic electron-positron plasma

Nonlinear equations for the interaction of the Langmuir wave field and the transverse electromagnetic field in the pulsar magnetosphere are derived. These equations take into account the modulational instability of plasma waves and its decay into two transversal waves.     

Solitons in a molecular chain with impurities

The propagation of Davydov's soliton in the molecular chain with an impurity has been investigated. The numerical analysis demonstrates that the presence of the impurity leads to the decreasing of the soliton velocity, as well as to the localization (pinning) of the excitation in a region of space close to the impurity or even to the reflection or destruction of the soliton. The analytical results which demonstrate that the influence of the impurity is equivalent to the existence of some localized external inhomogeneous field or friction force have been obtained also.