Tunneling resonances in structures with a two-step barrier

Electron transport through an asymmetric heterostructure with a two-step barrier N⁺GaAs/N⁻GaAs/Al_0.4Ga_0.6As/Al_0.03Ga_0.97As/N⁻GaAs/N⁺GaAs was investigated. Features due to resonance tunneling both through a size-quantization level in a triangular quantum well, induced by an external electric field in the region of the bottom step of the barrier (Al_0.03Ga_0.97As layer), and through virtual levels in two quantum pseudowells of different width are observed in the tunneling current. The virtual levels form above the bottom step or above one of the spacers (N⁻GaAs layer) as a result of interference of electrons, in the first case on account of reflection from the Al_0.4Ga_0.6As barrier and a potential jump at the Al_0.03Ga_0.97As/N⁻GaAs interface and in the second case — from the Al_0.4Ga_0.6As barrier and the potential gradient at the N⁻GaAs/N⁺GaAs junction, reflection from which is likewise coherent. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 814–819 (25 May 1998)     

Surface shape resonances of ridges on a thin film

The spectrum of surface shape resonances associated with a finite number of ridges on one interface of an otherwise plane film is calculated. The frequencies are obtained numerically by solving the homogeneous integral equations which describe the electrostatic field in the vicinity of a surface defect. The calculations are performed for a surface with ridges with Gaussian, Lorentzian and sinusoidal profiles. The results show a strong dependence of the localized plasmon frequencies on the surface profile, on the distance between the ridges, and on the thickness of the film. Received 5 April 1999 and Received in final form 6 July 1999     

Above barrier Dirac multiple scattering and resonances

We extend an above barrier analysis made with the Schrödinger equation to the Dirac equation. We demonstrate the perfect agreement between the barrier results and back to back steps. This implies the existence of multiple (indeed infinite) reflected and transmitted wave packets. These packets may be well separated in space or partially overlap. In the latter case interference effects can occur. For the extreme case of total overlap we encounter resonances. The conditions under which resonance phenomena can be observed is discussed and illustrated by numerical calculations.     

A one-dimensional model of resonances with a delta barrier and mass jump

In this Letter, we present a one-dimensional model that includes a hard core at the origin, a Dirac delta barrier at a point in the positive semiaxis and a mass jump at the same point. We study the effect of this mass jump in the behavior of the resonances of the model. We obtain an infinite number of resonances for this situation, showing that for the case of a mass jump the imaginary part of the resonance poles tend to a fixed value depending on the quotient of masses, and demonstrate that none of these resonances is degenerated.     

Surface plasmon dynamics of simple metal clusters excited with femtosecond optical pulses

We report a new mechanism on the dynamics of correlated electrons in simple metal clusters which manifests by a strong electron temperature dependence of the surface plasmon resonance spectral profile. This effect is revealed thanks to a theoretical approach based on the time-dependent local-density approximation at finite electronic temperature, and it should be experimentally observable using pump-probe femtosecond spectroscopy techniques.     

Square well/barrier resonances in the potentiodynamic plane

The complex wave number plane equips us with an elegant mathematical construct which can be used to display and classify the different types of states which arise from solution of the time-independent Schrödinger equation for a quantum mechanical potential. The complex wave number plane is also useful for tracking the trajectories of these solutions as the potential is perturbed in some way, often resulting in profound dynamical structure. In this work we propose an alternative coordinate system, which we call the potentiodynamic plane, which has the useful property that the trajectories stay bounded, and apply this to the square well/barrier potential to reveal some new insights.     

Perturbation theory for shape resonances and large barrier potentials

We develop a systematic perturbation and resonance theory for the one-dimensional Schrödinger equation of the form $$( - d^2 /dx^2 + U(x) + \lambda V(x) - E)\psi (x) = 0,0 \leqq x< \infty ,$$ where the barrier potentialV(x) is supported only wherex≧1 and is non-negative there, and λ is a real parameter tending to infinity. We prove that every λ=∞ eigenvalue turns into a resonance or an eigenvalue for finite λ.     

Physics of a metal-correlated barrier–metal heterostructure

We consider a heterostructure of a metal and a barrier with onsite correlation at half filling using the unrestricted Hartree–Fock method. We find that, above a certain value of correlation strength in the barrier planes, the system is an antiferromagnetic insulator, while below this value the system is gapless with no spin density wave order but still with considerable charge inhomogeneity being present across the planes. The energy spectrum is found to have multiple gaps as the correlation strength is increased. The system is insulating for values of correlation above the critical value at which the gap at half filling opens up.     

The surface susceptibility of a simple metal

The magnetic surface response of a simple metal to a uniform magnetic field is calculated for a jellium model of a metal surface. We find a positive surface contribution to the measured susceptibility of finite samples.     

Adatom mobility on the surface planes of a simple metal

An approach using the Density Functional Approximation, which had in an earlier paper been applied to the binding of an adatom to a jellium metal (r_s = 4a₀), has been extended to a partially structured metal surface by introducing a layer of surface atoms to replace an equivalent layer of jellium. The model has been used to estimate the adatom motion energies over several quite close packed planes for a simple surface. An important preliminary step was to determine the general electron density contours for each surface by a simple variational method. The ensuing shielding charge distributions have an important bearing on the adatom motion energy. Adatom energies were calculated at three positions: (1) A above a surface atom, (2) B above a bridge position between two surface atoms and (3) C above a central position between three or four neighboring atoms. The motion energy was taken to be E_B ? E_C. As might have been expected this quantity was larger for the less closely packed planes, although it was always quite small due to the nature of the metal — large r_S, small ion core and typical s-p binding. To a rather surprising degree the strength of the shielding charge, the energies and the positions of the adatoms proved to be quite smooth functions of a parameter chosen to measure the close packing of the surface, namely the square of the interplanar distance divided by the surface area per atom.     

Surface plasmons in a free-electron metal

The dispersion and damping of the surface plasmons are calculated for a free-electron model of Al. At large wave-vector the frequency of the surface plasmons approaches that of the bulk plasmons. Their damping remains quite small up to a wave-vector close to the bulk plasmon cut-off. The change in zero-point energy of the plasmons is calculated, and it gives a large positive contribution to the surface energy.     

Surface plasmon polariton coupling between a metal nanowire and a metal helix

The transmittance and steady-state electrical field distribution of a silver nanowire–helix system are investigated using the finite-difference time-domain method. In the nanowire–helix system, surface plasmon polaritons are coupled into the helix or squeezed into the space between the nanowire and helix. The transmittance strongly depends on the topologic shapes of the helix, especially the pitch height. Thus, the nanowire–helix system enables the detection of the displacement associated with helical deformation.