J. Krasnyj

Radius dependent shift in surface plasmon frequency in large metallic nanospheres: Theory and experiment

Theoretical description of oscillations of electron liquid in large metallic nanospheres (with radius of few tens of nanometer) is formulated within random-phase-approximation semiclassical scheme in jellium model with retardation included via Lorentz friction. Spectrum of plasmons is determined including both surface and volume type excitations. It is demonstrated that only surface plasmons of dipole type can be excited by homogeneous dynamical electric field. The Lorentz friction due to irradiation of electromagnetic wave by plasmon oscillations is analyzed with respect to the sphere dimension. The resulting shift in resonance frequency turns out to be strongly sensitive to the sphere radius. The form of electromagnetic (e-m) response of the system of metallic nanospheres embedded in the dielectric medium is found. The theoretical predictions are verified by a measurement of extinction of light due to plasmon excitations in nanosphere colloidal water solutions, for Au and Ag metallic components with rad...

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.

Undamped collective surface plasmon oscillations along metallic nanosphere chains

The random-phase-approximation semiclassical scheme for describing plasmon excitations in large metallic nanospheres (with radius ∼10–60u2002nm) is developed for the case when a dynamical electric field is present. The spectrum of plasmons in metallic nanospheres is determined including both surface and volume-type excitations and their mutual connections. It is demonstrated that only dipole-type surface plasmons can be excited by a homogeneous dynamical electric field. The Lorentz friction due to irradiation of electromagnetic energy by plasmon oscillations is analyzed with respect to sphere dimension. The resulting shift in resonance frequency due to plasmon damping is compared with experimental data for various sphere radii. Wave-type collective oscillations of surface plasmons in long chains of metallic nanospheres are described. The undamped region for collective plasmon propagation along the metallic chain is found in agreement with previous numerical simulations.

Plasmon-Polariton Properties in Metallic Nanosphere Chains

The propagation of collective wave type plasmonic excitations along infinite chains of metallic nanospheres has been analyzed, including near-, medium- and far-field contributions to the plasmon dipole interaction with all retardation effects taken into account. It is proven that there exist weakly-damped self-modes of plasmon-polaritons in the chain for which the propagation range is limited by relatively small Ohmic losses only. In this regime, the Lorentz friction irradiation losses on each nanosphere in the chain are ideally compensated by the energy income from the rest of the chain. The completely undamped collective waves were identified in the case of the presence of persistent external excitation of some fragment of the chain. The obtained characteristics of these excitations fit the experimental observations well.

Mechanism of plasmon enhancement of PV efficiency for metallic nano-modified surface of semiconductor photo-cell

Metallic nanospheres (Au, Ag, Cu) deposited on PV-active semiconductor surface can act as light converters, collecting energy of incident photons in plasmon oscillations. This energy can be next transferred to semiconductor substrate via a near-field channel, in a more efficient manner in comparison to the direct photo-effect. We explain this enhancement by inclusion of all indirect inter-band transitions in semiconductor layer due to 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 nano-sphere plasmon is formulated (RPA, analytical version, adjusted to description of large metallic clusters, with radius of 10-100 nm) including surface and volume modes. Damping of plasmons is analyzed including Lorentz friction, and irradiation losses in far- and near-field regimes. Resulting resonance shifts are verified experimentally for Au and Ag (10-80 nm) colloidal water solutions with respect to particle size. Probability of interband transition (within the Fermi golden rule) caused by coupling to plasmons in near-field regime turns out to be 4-order larger than for coupling of electrons to planar-wave photons. Inclusion of proximity effects (for type of deposition of nano-components and their shape) allows for explanation of photo-current growth experimentally measured. We describe also a non-dissipative collective mode of surface plasmons in a chain of near-field-coupled metallic nanospheres, for particular size/separation parameters and wave-lengths.

Spin qubit and its decoherence in QD in a diluted magnetic semiconductor medium

The spin degrees of freedom in quantum dots (QDs) of He‐type embedded in diluted magnetic semiconductor (DMS) medium are considered for modelling of qubit and gate for quantum information processing (QIP). The qubit is defined as a singlet and triplet pair of states of two electrons in He QD. Methods of qubit rotations and two‐qubit operations are considered. Decoherence due to spin waves in magnetically ordered phase of DMS is however recognized as the the source of unavoidable dephasing with inconvenient, from point of view of the DiVincenzo conditions, time‐scale.