Electronic correlations and conductivity for two coupled quantum wires

We study the effect of the interaction between two parallel wires on the electronic correlations and the conductivity of one of them. If the interactions are not singular and the wires are near enough, then we found that the correlations are quickly damped and a divergence in the conductivity at zero temperature appears. On the other hand, if the interactions are singular, then the correlations in each wire is not affected by the coupling with the other one.     

Nonlinear optical properties of semiconductor quantum wires

Nonlinear optical transmission at discrete frequencies (bleaching bands) has been observed in CdSe and GaAs quantum wires crystallized in chrysotile asbestos nanotubes with average diameter ≈ 6 nm and in nanocrystals of CdS (crystallized in the transparent molecular filter—mica with empty channels of designed diameter). The induced decrease of absorption in quantum wires has been explained by filling of the size-quantized energy bands with nonequilibrium carriers (saturation effect) and by the phase-space filling of excitons.     

Fabrication and optical properties of quantum dots and wires

We describe photoluminescence measurements made on mesa geometry quantum dots and wires with exposed side walls fabricated by laterally patterning undoped GaAs/AlGaAs quantum wells using electron beam lithography and dry etching. At low temperature the photoluminescence efficiency of many but not all of the GaAs quantum dot arrays scales with the volume of quantum well material down to lateral dimensions of 50nm. This behaviour contrasts with that found in wires produced at the same time where the intensity falls off rapidly with decreasing wire width for dimensions below 500nm but is recovered by overgrowth with indium tin oxide, possibly as a result of strain. Narrow overgrown wires exhibit anisotropy in polarized excitation spectra which is discussed in relation to strain and lateral confinement effects.     

Binding energy of localized trions in quantum wires

We present a finite difference calculation of the binding energies of localized trions in quasi-one-dimensional quantum wires (QWRs). It is found that both the lateral confinement and the localization potential have a strong effect on the relative stability of the trions. It is confirmed that a weak localization potential not only enhances the binding energy but also changes the relative stability of the positive and negative trions. Our theoretical model is in good accord with a recent experiment regarding photoluminescence in disordered QWRs.     

The optical Stark effect in semiconductor quantum wires

A new approach for controlling the optical emission wavelength of semiconductor quantum wires is proposed. The wavelength control resides upon the effect of an intense, long-wavelength laser field radiation applied to the semiconductor structure. Under such condition a strong optical Stark effect leads to optical tunability. Calculation of the optical Stark effect was carried out in the frame of the nonperturbative theory and finite difference method. Different geometries concerning the size of GaAs–AlGaAs quantum wires as well as the polarization direction and the strength of the applied laser field with respect to the quantum structure were considered.     

Polarization-dependent optical effects in open quantum well wires

We present a simple theory showing that open quantum well-wire structures demonstrate striking polarization-dependent optical effects. The reason for these effects is the inhomogeneous distribution of the electric component of electromagnetic field inside the nanostructure in cases when the field has components normal to the semiconductor/vacuum surface.     

Exciton states and optical absorption in quantum wires under laser radiation

We analyze the exciton states in a quantum wire under intense laser radiation. Electrons and holes are confined by the parabolic potential of the quantum wire. An exactly solvable model is introduced for calculating the exciton binding energy, replacing the actual Coulomb interaction between the electron and the hole by a projective operator.     

Saturation of optical transitions in quantum dots and wires of porous silicon

The bleaching bands have been observed in the time-resolved nonlinear transmission spectra of porous silicon. The increase of transmission at discrete frequencies has been attributed to a saturation of optical transitions between the energy levels of electrons and holes spatially confined within quasi-zero-dimensional (quantum dots) and quasi-one-dimensional (quantum wires) nanostructures. The results of independent measurements using transmission electron microscopy have confirmed the existence of quantum dots and wires of corresponding size. The slowed-down energy relaxation from upper to lower levels of size quantization compared with intraband relaxation in the bulk have been observed in the cooled (80K) platelets of porous silicon.     

Fermi energy of a metal nanowire with elliptical cross section

The influence of the geometrical shape of the cross section on the energy characteristics of a metal nanowire has been investigated theoretically. The size oscillations of the Fermi energy have been calculated within the model of an infinite potential well in terms of the perturbation theory. The calculations have been carried out for Au and Al. It has been shown that the cross-sectional ellipticity with a low eccentricity can be taken into account in the first-order perturbation theory by modifying the boundary conditions for the radial wave function of electrons.     

Electron-phonon interaction effect on optical absorption in cylindrical quantum wires

Electron-phonon interaction effects on linear and nonlinear optical absorption in cylindrical quantum wires are investigated. The linear and nonlinear optical absorption coefficients are obtained by using compact-density-matrix approach and iterative method, and the numerical results are presented for GaAs/AlAs cylindrical quantum-well wires. The results show that electron-phonon interaction not only influences the relaxation rate but also distinctly influences the wave functions and energies of the electron. The correction of electron-phonon interaction effect on the wave functions of the electron dominates the values of absorption coefficients. Moreover, the correction of electron-phonon interaction effect on the energies of the electron makes the absorption peaks blue shift and become wider.     

Fermi energy and electron thermopower in quantum films of an asymmetric profile

The behavior of the Fermi energy and the electron thermoelectric power in an asymmetric quantum well of the Morse potential type as a function of electron concentration are studied. It is shown that the Fermi energy is a piecewise-linear function, and the electron thermoelectric power is an oscillating function. The analysis shows that the nature of these oscillations differs significantly from that in films of a parabolic and rectangular profile, namely, the oscillation period is a nonmonotonic function and reaches a maximum at some value of the electron concentration. The possibility of estimating the parameters of the film profile (quantum well) is proposed. A comparison with the experiment shows a qualitative agreement.     

Intensity of intersubband electron scattering by polar optical phonons in semiconductor quantum wires with account of energy level broadening

An approach describing the effect of energy level broadening in semiconductor quantum wires on the intensity of intersubband electron scattering by polar optical phonons is suggested. As a broadening mechanism, scattering by atomic thermal vibrations and by the roughness of the confining surfaces of a quantum system is considered. It is shown that in this case the dependence of the intensity of intersubband scattering of electrons on their kinetic energy has no singularities.