Excitation of plasmonic nanoantennas by nonresonant and resonant electron tunnelling

Abstract

Abstract.A rigorous theory of photon emission accompanied inelastic tunnelling inside the gap of plasmonic nanoantennas has been developed. The disappointingly low efficiency of the electrical excitation of surface plasmon polaritons in these structures can be increased by orders of magnitude when a resonant tunnelling structure is incorporated inside the gap. Resonant tunnelling assisted surface plasmon emitter may become a key element in future electrically-driven nanoplasmonic circuits. I IntroductionPlasmonic nanoantennas attract much attention due to their ability at enhancing and controlling effectively the spontaneous emission rate of quantum emitters (molecules, quantum dots and so on) [1][2][3][4]. This unique asset has already been put into productive use in optically driven nanoantennas [3][4], primarily for sensing applications. But at the same time, the progress in integrated nanoplasmonic circuits has been impeded by the lack of efficient electrically-pumped sub-wavelength sources of light. For example, semiconductor lasers that enable present day photonic integrated topics suffer from high threshold and low efficiency when scaled down the sub-wavelength dimensions [5]. Given that, electrically-driven plasmonic nanoantennas appear to be a logical approach to the problem due to its apparent simplicity, as no nanoscale p-n junction needs to be formed and the light confinement is easily achieved in the vicinity of surface plasmon polariton (SPP) resonance.Excitation of plasmonic oscillations (both propagating and localized) with electron tunnelling is far from being a new topicit predates the first appearance of the term "plasmonics" by decades., but as we show below, it deserves a second look. Starting with the pioneering 1976 work [6] by Lambe and McCarthy, tunnelling excitation of surface plasmonic waves in planar Metal-Insulator-Metal (MIM) structures had been an object of plentiful experimental [6][7][8][9][10][11][12][13][14][15] and theoretical [16][17][18][19][20] studies. These investigations had been given an impetus by the invention of Scanning Tunnelling Microscope (STM) at the end of 1980's as numerous intensive studies of excitation of plasmonic modes with STM tips has been since performed [21][22][23][24][25][26][27][28][29]. With the advent of nanophotonics the focus of research on SPP electrical excitation has gradually shifted to the development of miniature light sources as can be learned from recent reports [30][31][32][33][34][35][36][37][38][39][40][41] and review [42] by García de Abajo.The results of the experimental measurements often differ from each other and from theoretical estimates by as much as an order of magnitude or more [30][31][32][33][34][35][36][37][38][39][40][41]. This is expected, given the great variety of experimental conditions as well as equally great diversity of theoretical approaches. Overall, though, it comes as no surprise that the most serious disadvantage of the electron tunnelling mechanism for the electrical excitation of SPP is its low quantum ef...

Optical antennas driven by quantum tunneling: a key issues review

“…Originally derived by Hone et al, equation (16) The third model describes IET as a spontaneous emission (SE) process, where the transitions occur within the tunnel junction and between electronic states of different energies [114][115][116][117][118][119]. Here, the rate of IET γ SE inel is determined by Fermi's golden rule…”

“…The further implementation varies in that the interaction Hamiltonian is either given byĤ int = −eφ, whereφ is the potential operator of the optical mode [94,[114][115][116], or byĤ int = −e/m ·p, where is the vector potential operator andp is the momentum operator [117][118][119].…”

“…This dependence may be explored in future devices to favor the inelastic process over the elastic process by bandstructure engineering. Alternatively, efficiencies may be increased by orders of magnitude in devices that support resonant inelastic electron tunneling [117,147]. Promising platforms for the realization of such strategies are molecular tunnel junctions [148,149] and van der Waals heterostructures [132,150,151].…”

Nanoantenna enhanced terahertz interaction of biomolecules

“…As the width of the gap (w) decreases further entering the sub-nanometer andÅngstrom regime, the charge distribution becomes insensitive to gap size and electron tunnels through the potential barrier of the nanogap, showing quantum effects. 197,[199][200][201][202][203][204][205][206][207][208][209][210] When THz electromagnetic waves are incident on the nanogap, a transient voltage is developed in the dielectric gap which bends the conduction band of the dielectric toward the Fermi energy of metals ( Fig. 9).…”

Biased Nanoscale Contact as Active Element for Electrically Driven Plasmonic Nanoantenna

“…4 The quest for an all-electrical source of SPPs had revived the interest in excitation of SPPs with tunneling electrons is recent years [5][6][7][8][9][10][11][12][13][14][15] . Thanks to that body of literature, there is a consensus on the underlying physics of SPP excitation in MIM structures (see [16][17] and references therein). With this understanding, the SPP is excited in the process of inelastic tunneling hence it is reasonable to refer to this process as "SPP-assisted tunneling".…”