Lucjan Jacak

Surface and volume plasmons in metallic nanospheres in a semiclassical RPA-type approach: Near-field coupling of surface plasmons with the semiconductor substrate

The random-phase-approximation semiclassical scheme for description of plasmon excitations in large metallic nanospheres, with radius range 10-60 nm, is formulated in an all-analytical version. The spectrum of plasmons is determined including both surface and volume type excitations and their mutual connections. The various channels for damping of surface plasmons are evaluated and the relevant resonance shifts are compared with the experimental data for metallic nanoparticles of different size located in dielectric medium or on the semiconductor substrate. The strong enhancement of energy transfer from the surface plasmon oscillations to the substrate semiconductor is explained in the regime of a near-field coupling in agreement with recent experimental observations for metallically nanomodified photo-diode systems.

Semiconductor quantum dots - towards a new generation of semiconductor devices

A short overview of the technology and physics of semiconductor quantum dots is given. Different methods of creation of quantum dots and mechanisms of carrier confinements are described. The fundamental properties of these systems are discussed including current attempts for applications in new ultra-small opto-electronic semiconductor devices.

Optimal strategy for a single-qubit gate and the trade-off between opposite types of decoherence

We study reliable quantum-information processing (QIP) under two different types of environment. The first type is Markovian exponential decay, and the appropriate elementary strategy of protection of qubit is to apply fast gates. The second one is strongly non-Markovian and occurs solely during operations on the qubit. The best strategy is then to work with slow gates. If the two types are both present, one has to optimize the speed of gate. We show that such a trade-off is present for a single-qubit operation in a semiconductor quantum dot implementation of QIP, where recombination of exciton (qubit) is Markovian, while phonon dressing gives rise to the non-Markovian contribution.

Hierarchy of fillings for the FQHE in monolayer graphene

In this paper, the commensurability conditions, which originated from the unique topology of two-dimensional systems, are applied to determine the quantum Hall effect hierarchy in the case of a monolayer graphene. The fundamental difference in a definition of a typical semiconductor and a monolayer graphene filling factor is pointed out. The calculations are undertaken for all spin-valley branches of two lowest Landau levels, since only they are currently experimentally accessible. The obtained filling factors are compared with the experimental data and a very good agreement is achieved. The work also introduces a concept of the single-loop fractional quantum Hall effect.

Cyclotron braid group structure for composite fermions

Although they describe properties of 2D Hall systems in the fractional quantum regime well, composite fermions suffer from the unexplained character of the localized magnetic field flux-tubes attached to each particle in order to reproduce the Laughlin correlations via Aharonov-Bohm phase shifts. The identification of the cyclotron trajectories of 2D charged particles as accessible classical trajectories within the braid group approach at the magnetic field presence, allows, however, for the avoidance of the construction with fluxes. We introduce cyclotron braid subgroups for charged 2D systems at the fractional Landau-level filling associated in a more natural way with composite fermions without invoking field flux-tubes. The Aharonov-Bohm phase shifts caused by fluxes are replaced with the phase gain due to multi-loop cyclotron trajectories unavoidably occurring at the fractional filling of 1/p (p is an odd integer). Another approach to composite particles, using so-called vortices, is also discussed from the point of view of the cyclotron braid group description (for both odd and even p integers).

Application of Braid Groups in 2D Hall System Physics: Composite Fermion Structure

Introduction Elements of Hall System Physics in 2D Spaces Topological Methods of Describing Systems of Many Particles at Various Manifolds Cyclotron Braids for Multi-Particle Charged 2D Systems in a Strong Magnetic Field Recent Progress in FQHE Field Summary Comments and Supplements.

Renormalization of the Fröhlich constant for electrons in a quantum dot

Recent experimental investigations of far-infrared attenuation in GaAs/InAs quantum dot in magnetic field and measurements of photoluminescence features for smaller pyramid-shape GaAs/InAs quantum dots indicated an enhancement of coupling of longitudinal optical phonons with confined electrons, which manifested itself in a significant increase of the effective Frohlich constant in comparison to its bulk value. We give a simple quasiclassical explanation of this enhancement and relate the renormalization of the Frohlich constant with the dot diameter.

Theory of luminescence from highly excited self-assembled quantum dots

The magneto-luminescence from lens-shaped self-assembled quantum dots, containing either many excitons or many electrons is studied. The single-electron and hole energy levels are shown to form degenerate shells in the absence of a magnetic eld. In the case of many-exciton dots, the hidden symmetries associated with these degeneracies are responsible for a remarkable dependence of the absorption=emission spectrum on the number of excitons. In the case of many-electron dots, the degeneracies lead to the Hund-like oscillation of the total spin as a function of the number of electrons, which can be probed by photoluminescence. The symmetry-breaking eect of a magnetic eld is also demonstrated. ? 1998 Elsevier Science B.V. All rights reserved.

Spin-orbit interaction in the quantum dot

The electronic states of a parabolic quantum dot in a magnetic field are studied with the inclusion of the spin-orbit interaction. The analytical formulae for the ground state energy of the interacting system are derived. The spin-orbit interaction is shown to introduce new features to the far infrared absorption spectrum, where it leads to the splitting of the two principal modes. The results are compared with the charging experiments by Ashoori et al. and the far infrared absorption measurements by Demel et al.

Mechanism of plasmon-mediated enhancement of photovoltaic efficiency

Metallic nanospheres (Au, Ag, Cu) deposited on a photovoltaic (PV)-active semiconductor surface can act as light converters, collecting energy of incident photons in plasmon oscillations. This energy can be next transferred to a semiconductor substrate via a near-field channel, in a more efficient manner in comparison with the direct photo-effect. We explain this enhancement by inclusion of indirect interband transitions in a semiconductor layer due to the near-field coupling with plasmon radiation in nanoscale of the metallic components, where the momentum is not conserved as the system is not translationally invariant. The model of the nanosphere plasmons is developed (random phase approximation, analytical version, adjusted to description of large metallic clusters, with a radius of 10–60 nm) including surface and volume modes. Damping of plasmons is analysed via Lorentz friction, and irradiation losses in the far- and near-field regimes. Resulting resonance shifts are verified experimentally for Au and Ag colloidal water solutions with respect to particle size. Probability of the electron interband transition (within the Fermi golden rule) in the substrate semiconductor induced by coupling to plasmons in the near-field regime turns out to be significantly larger than for coupling of electrons to planar-wave photons. This is of practical importance for enhancement of thin-film solar cell efficiency, both for semiconductor type (such as III–V semiconductor based cells) and for conjugate-polymer-based or dye organic plastic cells, intensively developed at present. We have described also a non-dissipative collective mode of surface plasmons in a chain of near-field-coupled metallic nanospheres, for particular size, separation parameters and wavelengths. This would find an application in sub-diffraction electro-photonic circuit arrangement and for possible energy transport in solar cells, in particular in organic materials with low mobility of carriers.