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Terahertz (THz) response spectra of GaN-based field-effect transistor (FET) arrays are calculated in a self-consistent electromagmetic approach. Two types of FET arrays are considered: (i) FET array with a common channel and a large-area grating gate, and (ii) array of FET units with separate channels and combined intrinsic source and drain contacts. It is shown that the coupling between plasmons and THz radiation in the FET array can be strongly enhanced as compared to a single-unit FET. The computer simulations show that the higher-order plasmon modes can be excited much more effectively in the array of FET units with separate channels and combined source and drain contacts then in FET array with a common channel and a large-area grating gate.

This paper gives a survey of physical phenomena manifesting themselves in electron and photon collisions with atomic clusters. The emphasis is made on electron scattering, photoabsorption and photoionization of fullerenes and metal clusters, however some results are applicable to other types of clusters as well. It is demonstrated that the diffraction and interference phenomena play an important role in the processes of clusters interaction with photons and electrons. The essential role of the multipole surface and volume plasmon excitations is elucidated in the formation of electron energy loss spectra on clusters as well as in the total inelastic scattering cross sections and in multiphoton absorption regime. Attention is paid to the elucidation of the role of the polarization interaction in low energy electron-cluster collisions. This problem is considered for the electron attachment to metallic clusters and the plasmon enhanced photon emission. The mechanisms of electron excitation widths formation and the relaxation of electron excitations in metal clusters and fullerenes are discussed.

Two-dimensional electrons in graphene are known to behave as massless fermions with Dirac-Weyl type linear dispersion near the Dirac crossing points. We have investigated the collective excitations of this system in the presence or absence of an external magnetic field. Unlike in the conventional two-dimensional electron system, the fractional quantum Hall state in graphene was found to be most stable in the n = 1 Landau level. In the zero field case, but in the presence of the spin-orbit interaction, an undamped plasmon mode was found to exist in the gap of the single-particle continuum.

The effect of space symmetry on magnetoplasmon charge density excitations in a weekly tunnel coupled bilayer electron system is considered. The magnetic field corresponds to the filling factor ν = 4. The energy of optic magnetoplasmon is not affected by space symmetry. Three other collective magnetoplasmon modes are determined by relations between parameters of asymmetry, tunnel parameter and energy of acoustic plasmon.

Microwave (MW) absorption by a high mobility 2DEG has been investigated experimentally using sensitive Electron Paramagnetic Resonance (EPR) cavity technique. It is found that MW absorption spectra are chiefly governed by confined magnetoplasmon excitations in a 2DEG stripe. Spectra of the 2D magnetoplasmons are studied as a function of magnetic field, MW frequency and carrier density. The electron concentration is tuned by illumination and monitored using optical photoluminescence technique.

We calculate the dielectric function of a Weyl semimetal at arbitrary momentum q and frequency ω within the random-phase approximation. Taking the static limit, we calculated the Friedel oscillation and found that: (1) For a single Weyl point, the oscillation ~sin(2k_Fr)/r⁴ falls off faster by an 1/r factor than the one in traditional 3D systems ~cos(2k_Fr)/r³. This difference arises from the suppression of backward scattering in Weyl fermion systems; (2) For Weyl semimetal with two Weyl points, there are additional oscillations decaying as cos(Q ⋅ r)/r³ and cos(Q ± 2k_F) ⋅ r/r³, where Q is the momentum difference between the two Weyl points. We also calculated the plasmon dispersion and found features distinct from those of conventional 3D metals.

We investigate the plasmon mode coupling and depolarization shifts in AlGaAs/GaAs asymmetric step quantum wells (ASQWs) of the two-subband model with the Bohm–Pine’s random-phase approximation with and without an applied electric field. By adjusting the well geometry parameters and material composition systematically, various characteristics of plasmons in ASQWs are found for different asymmetric cases. We find that (i) the intersubband plasmon has a large negative dispersion in long wavelength limit; (ii) the step width related depolarization shift depends on the number of subbands in the deep well; and (iii) the influence of electric field effect on depolarization shift and the coupling of the two plasmon modes is quite asymmetric with its minimum at +8 kV/cm by changing the electrical field and the ASQW structure parameters. The coupling and decoupling of the intersubband and intrasubband plasmon modes can be realized by adjusting the polarity and the strength of the external electric field and changing the ASQW structure parameters.

In this paper, we review the theory of open quantum systems and macroscopic quantum electrodynamics, providing a self-contained account of many aspects of these two theories. The former is presented in the context of a qubit coupled to a electromagnetic thermal bath, the latter is presented in the context of a quantization scheme for surface-plasmon polaritons (SPPs) in graphene based on Langevin noise currents. This includes a calculation of the dyadic Green’s function (in the electrostatic limit) for a Graphene sheet between two semi-infinite linear dielectric media, and its subsequent application to the construction of SPP creation and annihilation operators. We then bring the two fields together and discuss the entanglement of two qubits in the vicinity of a graphene sheet which supports SPPs. The two qubits communicate with each other via the emission and absorption of SPPs. We find that a Schrödinger cat state involving the two qubits can be partially protected from decoherence by taking advantage of the dissipative dynamics in graphene. A comparison is also drawn between the dynamics at zero temperature, obtained via Schrödinger’s equation, and at finite temperature, obtained using the Lindblad equation.

Ultrathin Ag and Ni/NiO films are sequentially produced on Corning glass and silicon substrates by means of magnetron sputtering. Post annealing treatment in a furnace with air at $420^{\circ }$C and $500^{\circ }$C may lead to the formation of Ag nanostructures in NiO environment. Some of these samples present local surface plasmon resonances (SPRs). The sequence in which each layer is deposited, as well as, the state of the structure on which the layer is deposited, appears to play a pivotal role in the optical properties of these nanostructures, which are attributed to the growth properties of the nanocomposite thin films. Ultimately, rigorous theoretical calculations have been made for comparison and discussion with the experimental results.

In this paper, we calculate a self-contained theoretical analysis of the dynamical response of the electron system in the fractional dimensional space within the random phase approximation. We find the static response function in several integer and non-integer dimensions. The plasma frequencies except in the quasi-one-dimensional system are damped into particle–hole excitation. In the long-wavelength limit the plasma frequency is finite at zero wave vector in three-dimensional system while these vanish at the same wave vector in the lower-dimensional systems.

We have studied the effect of temperature on static density–density correlations and plasmon excitation spectrum of quasi-one-dimensional electron gas (Q1DEG) using the random phase approximation (RPA). Numerical results for static structure factor, pair-correlation function, static density susceptibility, free exchange-correlation energy and plasmon dispersion are presented over a wide range of temperature and electron density. As an interesting result, we find that the short-range correlations exhibit a non-monotonic dependence on temperature T, initially growing stronger (i.e. the pair-correlation function at small inter-electron spacing assuming relatively smaller values) with increasing T and then weakening above a critical T. The cross-over temperature is found to increase with increasing coupling among electrons. Also, the $q=2k_F$ peak in the static density susceptibility $\chi (q,\omega =0,T)$ at T = 0 K smears out with rising T. The free exchange-correlation energy and plasmon dispersion show a significant variation with T, and the trend is qualitatively the same as in higher dimensions.

Reflected and transmitted powers due to the interaction of electromagnetic waves with a structure containing thin metal and silicon layer are investigated in more detail. The formulations for the transverse electric wave case are provided. Transfer matrix method is used to find the reflection and the transmission coefficients at each interface. Numerical results are presented to show the effect of the structure parameters, the incidence angle and the wavelength on the reflected, transmitted and loss powers.

The electronic plasmons of single layer MoS₂ induced by different spin subbands owing to spin-orbit couplings (SOCs) are theoretically investigated. The study shows that two new and anomalous plasmonic modes can be achieved via inter-spin subband transitions around the Fermi level due to the SOCs. The plasmon modes are optic-like, which are very different from the plasmons reported recently in single-layer (SL) MoS₂, and the other two-dimensional systems. The frequency of such plasmons ascends with the increasing of electron density or spin polarizability, and decreases with the increasing of wave vector. The promising plasmonic properties of SL MoS₂ make it interesting for future applications in plasmonic and terahertz devices.

Photoabsorption profiles of copper clusters, Cu_N, grown in superfluid helium droplets were studied by beam depletion spectroscopy. For N below ~ 10³ the spectra are characteristic of individual metallic particles, but in larger clusters a strong, broad absorption feature appears in the near-infrared region. This suggests a transition from single- to multicenter condensation: as the arrival frequency of metal atoms exceeds their transport time within the helium matrix, they nucleate into small individual agglomerates which later collect into a noncompact, possibly fractal or percolative assembly. The data, in concert with earlier observations on silver cluster growth, affirm that the formation of cluster–cluster aggregates with unusual optical properties is a general phenomenon achievable with the use of the helium nanodroplet technique.

We analyze the photoluminescence intermittency (blinking) of single colloidal CdSe/ZnS quantum dots (QDs). Two distinct emission levels, a bright on-state and a low-intensity gray state, correspond to monoexponential decay times of 58ns and 4ns, respectively. The ratio gray/on states increases upon increasing excitation intensity. Conversely, the gray/on level intensity ratio increases upon coupling to a plasmonic nanostructure, while the states maintain their monoexponential character. Corroborated by data from a CdSeTe/ZnS QD, our results demonstrate that type I QDs can indeed show a gray (rather than completely dark) emission level with a distinct monoexponential decay, a point that is discussed controversially in the literature.

Terahertz (THz) response spectra of GaN-based field-effect transistor (FET) arrays are calculated in a self-consistent electromagmetic approach. Two types of FET arrays arc considered: (i) FET array with a common channel and a large-area grating gate, and (ii) array of FET units with separate channels and combined intrinsic source and drain contacts. It is shown that the coupling between plasmons and THz radiation in the FET array can be strongly enhanced as compared to a single-unit FET. The computer simulations show that the higher-order plasmon modes can be excited much more effectively in the array of FET units with separate channels and combined source and drain contacts then in FET array with a common channel and a large-area grating gate.