N C Constantinou

Effects of finite well depth on polar optical phonon scattering rates in cylindrical quantum well wires

An investigation of the effects of a finite confining potential on the sub-band energies and electron-bulk-polar-optical-phonon scattering rates is presented within the effective-mass approximation for quasi-one-dimensional cylindrical quantum wires. Numerical results are given for the GaAs/AlGaAs system where a lowering of both the confined energies and electron-bulk-polar-optical-phonon scattering rates with respect to the widely used infinite-confining-potential approximation is found.

General linear response theory of polaritons in binary superlattices

A general fully retarded theory of polaritons in a two-component (binary) dielectric superlattice is developed using linear response techniques. The polariton Green functions of the superlattice are derived explicitly assuming arbitrary forms for the isotropic dielectric functions of the superlattice components. From these Green functions the dispersion relations and spectral intensities for transverse electric and transverse magnetic polariton models in the superlattice may be deduced. Some numerical illustrations are included. The results of the general theory are verified to yield correct forms in various known special cases. The authors also deduce the form of the Green functions in the nonretarded approximation, anticipating subsequent application of the theory to light scattering by low-frequency plasmon-polaritons in semiconductor superlattices.

The interaction of electrons with optical phonons in embedded circular and elliptical GaAs quantum wires

We consider electronic intrasubband transitions involving the confined and interface optical phonons of circular and elliptical GaAs quantum wires. Detailed treatments are given for a GaAs wire embedded in AlAs where the electrons are confined via an infinite potential barrier. The optical phonons are described using the dielectric continuum (DC) model, which for the GaAs/AlAs system compares favourably with more sophisticated macroscopic models and ab initio microscopic calculations in its prediction for the total scattering rates. The DC model has been applied previously to the circular case, bur here we evaluate the rates analytically. It is shown that the behaviour of the electrons and phonons in elliptical wires is both quantitatively and qualitatively different from that in circular wires, especially as regards angular properties.

The effective-medium theory of magnetoplasma superlattices

The expression for the effective-medium dielectric tensor of a superlattice in which the dielectric tensors of the constituent media are taken in general form (all elements non-zero) is employed to describe a plasma/non-plasma, e.g. doped/undoped semiconductor superlattice in a magnetic field B0 at an arbitrary angle to the interface. The properties of surface polaritons are discussed in detail for the perpendicular (B0 normal to interfaces) and Faraday (B0 parallel to interfaces, propagation vector along B0) configurations.

Green-function theory of light scattering from plasmons in a superlattice with electron-gas layers

Abstract Linear response theory is employed to calculate the Green functions describing the plasma modes in a superlattice of two-dimensional electron-gas layers separated by an isotropic dielectric medium. Applications are made to inelastic light scattering from the plasma modes, and we give expressions for the spectral lineshape and integrated intensity. Numerical results are obtained for GaAs Al x Ga 1 − x As superlattices,allowing comparison with experimental data.

Bulk and surface plasmon modes in a superlattice of alternating layered electron gases

Calculations are presented for the collective plasmon modes of a superlattice consisting of two-dimensional electron gas layers separated by media of alternating thickness and/or dielectric constant. The theory is developed for bulk plasmon modes in an infinite superlattice, and for bulk and surface modes in a semi-infinite superlattice. Applications are made to layered electron gases in semiconductor heterojunctions (such as GaAs/AlxGa1-xAs), and in particular to light scattering from the plasmons.

Effects of finite charge-layer thickness in Raman scattering by plasmons in semiconductor superlattices

Abstract A response-function theory of light scattering by plasmons in the bulk of semiconductor superlattices is employed to study effects due to the finite thickness of the charge layers. It is shown that in the non-retarded limit of this theory there may be two low-frequency plasmon peaks in the light scattering spectrum, compared with only one bulk plasmon peak in the two-dimensional charge sheets model of semiconductor superlattices. The spectral lineshapes and intensities corresponding to the plasmon excitations are calculated. This theory is applied in particular to GaAs/ AlxGa1-xAs superlattices, allowing comparison with experimental data.

Dispersion of superlattice optical phonons

Abstract Microscopic models of longwavelength zone-centre optical modes in superlattices predict an anisotropic behaviour of the dipole active modes. Recent micro-Raman data has unambiguously demonstrated this anisotropy for LO1 and it is shown here that a continuum model that simply mixes confined LO and interface modes gives very good agreement with the data.

The critical field of a hollow type-II superconducting cylinder

An exact calculation is given of the upper critical field of a hollow isotropic type-II superconducting cylinder. This field is the analogue of the surface-sheath critical field Hc3. As the temperature decreases below Tc the critical field corresponds to increasing values of the azimuthal quantum number mod m mod , i.e. the fluxoid number. The results are compared with those for a flat surface, a film and a solid cylinder and with the approximate result for a thin-walled cylinder. For the last case, it is shown bow the Little-Parks oscillations are modified as the cylinder wall thickness increases. The effects of normal-metal cladding on the inner and outer surfaces are calculated.

The Zeeman splitting of quasi-one dimensional electron subbands

The subband energy levels of an electron confined in one dimension by a cylindrically symmetric square well potential (both infinite and finite) are investigated within the effective-mass approximation as a function of magnetic field applied along the cylinder axis. For small fields the doubly degenerate states ( mod m mod >0), where m is the azimuthal quantum number, are Zeeman split with subbands have m>0 shifting to higher energies whilst those with m<0 initially decrease in energy. A minimum in the energy of the negative-m states is predicted. This minimum occurs whatever the specific form of the confining potential, the only proviso being that it is cylindrically symmetric. This effect is intimately related to the number of elementary flux quanta Phi o(=h/e) contained within the electrons cyclotron orbit.