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Optical Tunability of Silver-Dielectric-Silver Multi-Layered Cylindrical Nanotubes Using Quasi-Static Approximation
摘要： Local surface plasmon resonances (LSPRs) of silver-dielectric-silver multi-layered (SDS-ML) nanotubes are studied by theoretical calculations. Based on quasi-static approximation, the absorption cross section of SDS-ML nanotubes is plotted as a function of wavelength. The results show that SDS-ML nanotubes exhibit strong coupling between the cylindrical silver and nanotubes. The absorption spectra of LSPRs are strongly influenced by changing the radius of the inner core and outer nanotube shell. The longer wavelength is red-shifted by increasing the radius of the inner core and outer shell, while the short wavelength shows the opposite properties. These phenomena are explained by the plasmon hybridization theory. In addition, for clarity, the distributions of electric field intensity at their plasmon resonance wavelengths are also studied.
关键词： Local surface plasmon resonances,quasi-static approximation,silver-dielectric-silver multi-layered nanotubes,plasmon hybridization theory
更新于2025-09-09 09:28:46
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High-energy direct photoelectron spectroscopy in strong-field ionization
摘要： Recently, in the tunneling regime of strong-field ionization an unexpected Coulomb field effect has been identified by numerical solution of the time-dependent Schr?dinger equation [Phys. Rev. Lett. 117, 243003 (2016)] in photoelectron spectra in the upper energy range of the direct electrons. We investigate the mechanism of the Coulomb effect employing a classical theory with Monte Carlo simulations of trajectories, and a quantum theory based on the generalized eikonal approximation for the continuum electron. The effect is shown to have a classical nature and is due to momentum space bunching of photoelectrons released not far from the peak of the laser field. Moreover, our analysis reveals specific features of the angular distribution of high-energy direct electrons, which can be employed for molecular imaging. For the H2+ molecule as an example we show the signatures of the molecule orientation and the molecular structure in the investigated angular distribution.
关键词： Coulomb field effect,generalized eikonal approximation,photoelectron spectra,strong-field ionization,molecular imaging
更新于2025-09-09 09:28:46
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Enhanced performance of a quantum-dot-based nanomotor due to Coulomb interactions
摘要： We study the relation between quantum pumping of charge and the work exchanged with the driving potentials in a strongly interacting ac-driven quantum dot. We work in the large-interaction limit and in the adiabatic pumping regime, and we develop a treatment that combines the time-dependent slave-boson approximation with linear response in the rate of change in the ac potentials. We find that the time evolution of the system can be described in terms of equilibrium solutions at every time. We analyze the effect of the electronic interactions on the performance of the dot when operating as a quantum motor. The main two effects of the interactions are a shift of the resonance and an enhancement of the efficiency with respect to a noninteracting dot. This is due to the appearance of additional ac parameters accounting for the interactions that increase the pumping of particles while decreasing the conductance.
关键词： slave-boson approximation,quantum pumping,quantum dot,adiabatic pumping regime,quantum motor,electronic interactions
更新于2025-09-09 09:28:46
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[Advances In Atomic, Molecular, and Optical Physics] Volume 66 || Efficient Description of Bose–Einstein Condensates in Time-Dependent Rotating Traps
摘要： Quantum sensors based on matter-wave interferometry are promising candidates for high-precision gravimetry and inertial sensing in space. The favorable sources for the coherent matter waves in these devices are Bose–Einstein condensates. A reliable prediction of their dynamics, which is governed by the Gross–Pitaevskii equation, requires suitable analytical and numerical methods, which take into account the center-of-mass motion of the condensate, its rotation, and its spatial expansion by many orders of magnitude. In this chapter, we present an efficient way to study their dynamics in time-dependent rotating traps that meet this objective. Both an approximate analytical solution for condensates in the Thomas–Fermi regime and dedicated numerical simulations on a variable adapted grid are discussed. We contrast and relate our approach to previous alternative methods and provide further results, such as analytical expressions for the one- and two-dimensional spatial density distributions and the momentum distribution in the long-time limit that are of immediate interest to experimentalists working in this field of research.
关键词： Bose–Einstein condensates,Thomas–Fermi approximation,matter-wave interferometry,Gross–Pitaevskii equation,quantum sensors
更新于2025-09-09 09:28:46
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[IEEE 2018 Conference on Emerging Devices and Smart Systems (ICEDSS) - Tiruchengode, India (2018.3.2-2018.3.3)] 2018 Conference on Emerging Devices and Smart Systems (ICEDSS) - A Comparison of Analytical Modeling of Double Gate and Dual material Double GateTFETs with high-KStacked Gate-Oxide Structure forLow power Applications
摘要： In this paper, an analytical comparative study of Double Gate Tunnel Field Effect Transistors(DG-TFETs) and Dual Material Double Gate Tunnel Field Effect Transistors(DMDG-TFETs) with high-K stacked gate oxide structure are presented. The modeling is done by solving the Poisson’s equation with Parabolic Approximation Technique with suitable boundary conditions. By using channel potential model, Surface potential is calculated.The Drain current model is developed by integrating band to band tunneling generation rate. The different electrical characteristics like surface potential, Electric field and Drain current have been compared for both TFETs in this paper. On comparing DG-TFETs with Dual material, DMDG-TFETs provide an enhanced performance. The analytical results are also compared with TCAD simulated results for both the devices and good agreement is observed.
关键词： Band-to-band tunneling (BTBT),Tunnel FET (TFET),Dual-material (DM) gate,Parabolic Approximation Technique
更新于2025-09-09 09:28:46
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Acceleration techniques in a bi-iterative model for EM scattering from a 3-D object above a 2-D rough surface
摘要： A novel bi-iterative model is proposed to solve the extra large-scale composite electromagnetic (EM) scattering from an object above a rough surface. For the rough surface scattering, the forward-backward methodology and its modi?cation with under-relaxation iteration method are developed to accelerate the convergence of the iterative physical optics (IPO) and improve its robustness. Meanwhile, the local iteration methodology and the fast far ?eld approximation (FaFFA) in the matrix-vector product are proposed to reduce effectively the computational complexity and further improve the ef?ciency of the whole iteration process. Hence, this model can greatly reduce the computational costs, including both RAM memory and CPU time.
关键词： under-relaxation iteration,EM scattering,target above rough surface,fast far ?eld approximation
更新于2025-09-09 09:28:46
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Bulk and surface plasmons in graphene finite superlattices
摘要： In recent years, graphene plasmonics, has attracted significant interest motivated by graphene's unique high carrier mobility, electrically or chemically tunable carrier density, long-lived and strong plasmon excitation confinement. In the context of optoelectronics and nanophotonics, graphene is considered as promising plasmonic material working in the mid-infrared and terahertz spectral windows. However, in a single layer graphene, the electromagnetic energy has a limited capability to plasmon excitations. To obtain a more powerful capacity of excite plasmon resonance, one can employ multilayer graphene structures as possible solution. In this work, we find an analytical expression for the dielectric function of the N-layer graphene structure solving a recurrence relation between the electric potential at different graphene layers. We also find that the highest energy of the plasmon oscillations supported by the multilayer graphene stacks at long wavelength correspond to electrons in each plane oscillating in phase. In addition, a surface plasmon mode emerges at certain finite wave vector outside the bulk plasmon band and it is Landau damping in the continuous interband single particle excitation with increasing wave vector.
关键词： Recursive approximation,Graphene,Plasmons in finite superlattices
更新于2025-09-09 09:28:46
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Phonon thermodynamics and elastic behavior of GaN at high temperatures and pressures
摘要： The effects of temperature and pressure on the phonons of GaN were calculated for both the wurtzite and zinc-blende structures. The quasiharmonic approximation (QHA) gave reasonable results for the temperature dependence of the phonon DOS at zero pressure but unreliably predicted the combined effects of temperature and pressure. Pressure was found to change the explicit anharmonicity, altering the thermal shifts of phonons and more notably qualitatively changing the evolution of phonon lifetimes with increasing temperature. These effects were largest for the optical modes, and phonon frequencies below approximately 5 THz were adequately predicted with the QHA. The elastic anisotropies of GaN in both wurtzite and zinc-blende structures were calculated from the elastic constants as a function of pressure at 0 K. The elastic anisotropy increased with pressure until reaching elastic instabilities at 40 GPa (zinc blende) and 65 GPa (wurtzite). The calculated instabilities are consistent with proposed transformation pathways to rocksalt GaN and place upper bounds on the pressures at which wurtzite and zinc-blende GaN can be metastable.
关键词： phonon thermodynamics,high pressures,elastic anisotropy,anharmonicity,high temperatures,GaN,elastic behavior,quasiharmonic approximation
更新于2025-09-09 09:28:46
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First-principles study of structural phase transformation and dynamical stability of cubic AlN semiconductors
摘要： Phase transformation and stability of cubic aluminium nitride (AlN) phases such as zinc-blende and rock-salt have been investigated using first-principles calculations based on density functional perturbation theory (DFPT) within quasi-harmonic approximation (QHA). The phonon dispersion relations of both the cubic phases have been calculated at various high-symmetry points of the Brillouin Zone. The pressure and volume dependence of phonon frequencies have been investigated. The application of pressure results in opposite trend of transverse acoustic (TA) phonon frequencies for rock-salt and zinc-blende AlN phases. The TA frequencies found to increase for the former one and decrease for the latter one with the increase in pressure. The dynamical instability results in a volume expansion of rock-salt AlN close to the equilibrium volume of zinc-blende AlN. Phase transformation of these cubic phases is further investigated by computing an equilibrium pressure-temperature phase diagram within QHA. The cubic rock-salt AlN is found to form at high pressures and temperatures than zinc-blende AlN. The temperature dependence of lattice constant and the corresponding volume thermal expansion coefficient of both the cubic phases have been investigated.
关键词： Aluminium nitride,First-principles calculations,Density functional perturbation theory,Quasi-harmonic approximation,Phase transformation,Dynamical stability
更新于2025-09-09 09:28:46
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Multiphonon Intracenter Relaxation of Boron Acceptor States in Diamond
摘要： The relaxation rates are calculated in the adiabatic approximation, in which the steady-state impurity states are taken to be electronic-vibrational (vibronic) states. The probabilities of transitions between these states with the emission (or absorption) of one or several phonons are calculated in first-order perturbation theory on the assumption that the transitions are a result of the violation of adiabaticity. The electron part of the wave function of the vibronic state is described by a simple Hamiltonian with an isotropic effective mass. The wave function of the ground state is determined by the quantum defect method. According to the calculations, a hole relaxes from the excited boron acceptor state, whose energy is 304 meV higher than the energy of the ground state, to the ground state with the emission of two optical phonons with a rate of ~1011 s–1. This value is an estimate from above, since the model of nondispersive optical phonons used in the study overestimates the number of phonon modes, whose participation in relaxation is allowed by the energy conservation law. However, despite the rough approximation, it can be concluded that the multiphonon relaxation of boron acceptor states in diamond is a fast process.
关键词： diamond,boron acceptor states,multiphonon relaxation,vibronic states,adiabatic approximation
更新于2025-09-09 09:28:46