Nonlocal plasmon excitation in metallic nanostructures

Abstract

We investigate the excitation of electrostatic wakefields in metallic nanostructures (nanowires) due to the propagation of a short electron pulse. For that purpose, a dispersive (nonlocal) dielectric response of the system is considered, accounting for both the finiteness of the system and the quantum (Bohm) difraction of the conduction electron band, generalizing the results obtained previously in the literature [Phys. Rev. Lett. 103, 097403 (2009)]. We discuss on the stability conditions of wakefields and show that the underling mechanism can be useful to investigate new sources of radiation in the extreme-ultra-violet (XUV) range.Experimental techniques [1] have been developed for the fabrication of metallic nanostructures (nanowires) of the order of 10 nm or less, recently receiving a considerable attention of the scientific community. Nanowires, compared to other low-dimensional systems, have two conned directions, still leaving one unconned direction for electrical conduction. Due to their unique density of states, such systems are expected to exhibit significantly different optical, electrical, and magnetic properties from their bulk 3D crystalline counterparts, specially in the limit of small diameters. Even if the number of electrons involved in the relevant features is high, and therefore a continuum description is expected to be adequate, the current models still lack of completeness. One of the most striking cases is related with the dielectric response. It was experimentally shown that anomalous absorption can occur in thin metal films [2] due to the excitation of plasmons [3]. Liu et al. [4] have recently approached this problem for arbitrarily shaped nanostructures, though neglecting the wavenumber dependence in their model. Recently, McMahon et al [5] have introduced the effects of the nonlocal response by adding dispersion terms (proportional to the wavevector k) in the Drude dielectric function of the bulk (conduction) electrons, as described bywhere ∞ (≈ 1) is the value for ω → ∞, ω p and v F stand for the plasma frequency and the electron Fermi velocity, respectively, and γ represents the electron collision frequency. However, it is well known that further quantum mechanical effects [6] are associated with electrons at nanoscales, playing a significant role in the dispersion of collective modes and instabilities, and therefore are expected to play an important role in nanowires, as well. In particular, such quantum effects become important when the thermal wavelength is comparable to the typical dimensions of the system. In this Letter, we extend the dispersive Drude model in order to cast these quantum corrections and derive a nonlocal dielectric constant for quasi one-dimensional nanostructures (nanowires). More specifically, we take into account the effects of i) the finiteness of the system along the transverse direction and ii) the quantum diffraction (Bohm potential) due to a gradient of the electronic density. We then apply our result to investigate the excitation of wakefields due to...

An Introduction to Quantum Plasmas

“…We can nonetheless gain some insight on the interpretation of the ensemble wavefunctions. From (31) and (33), we see that…”

“…The fermionic character of the system is not necessarily included, but this can be done by assuming the N-body ensemble wavefunctions to be antisymmetric in (31). Wigner functions provide a convenient mathematical tool to calculate average quantities, and hence are analogous to the classical probability distribution function.…”

Exciton-polariton wakefields in semiconductor microcavities

“…We notice the that slow and fast oscillations propagate with the same phase velocity, which equals the velocity v of the moving source. Such a synchronism between the velocity of the moving object and the phase velocity of the wakefield oscillations is a characteristic features of the wakefields [30,35]. One interesting application of wakefields in practical experiments can be the characterization of semi-conductor micro-cavities, as the form of the wake is strictly related on the basic properties of the semi-conductor and the cavity (quality factor, excitonic life-time, coupling strength, etc).…”

“…Acoustic wakefields produced by a Bose-Einstein condensate moving across a thermal (non-condensed) gas has also been considered [33,34]. Recently, wakefield excitation in metallic nanowires has also been investigated and pointed out as mechanism to produce energetic ultra-violet (XUV) radiaton [35]. In the present work, we show that a similar process can occur in a gas of excitons and excitonarXiv:1402.1301v1 [cond-mat.mes-hall] 6 Feb 2014 polaritons (we should refer to the latter as "polaritons"), depending on the point of the dispersion that the system is pumped.…”

Pseudorelativistic effects on solitons in quantum semiconductor plasma

“…The collective effect plays a crucial role in the investigation of electron dynamics on an ultrafast time scale [15], As the 'ylwang@ustb.edu.cn short electron pulse propagates in the metallic nanowires, the stable wake field may be excited for a reasonable set of experimentally accessible parameters, which can be used to produce radiation in the extreme-ultraviolet range [16].…”