Active control of ultrafast electron dynamics in plasmonic gaps using an applied bias

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Active control of ultrafast electron dynamics in plasmonic gaps using an applied bias

Markus Ludwig, Andrey K. Kazansky, Garikoitz Aguirregabiria, Dana Codruta Marinica, Matthias Falk, Alfred Leitenstorfer, Daniele Brida, Javier Aizpurua, and Andrei G. Borisov

Phys. Rev. B 101, 241412(R) – Published 24 June 2020

Abstract

In this joint experimental and theoretical study we demonstrate coherent control of the optical field emission and electron transport in plasmonic gaps subjected to intense single-cycle laser pulses. Our results show that an external THz field or a minor dc bias, orders of magnitude smaller than the optical bias owing to the laser field, allows one to modulate and direct the electron photocurrents in the gap of a connected nanoantenna operating as an ultrafast nanoscale vacuum diode for lightwave electronics. Using time-dependent density functional theory calculations we elucidate the main physical mechanisms behind the observed effects and show that an applied dc field significantly modifies the optical field emission and quiver motion of photoemitted electrons within the gap. The quantum many-body theory reproduces the measured net electron transport in the experimental device, which allows us to establish a paradigm for controlling nanocircuits at petahertz frequencies.

Received 18 February 2020
Accepted 8 June 2020

DOI:https://doi.org/10.1103/PhysRevB.101.241412

Physics Subject Headings (PhySH)

Density functional theory Light-matter interaction Photoemission Plasmonics Strong electromagnetic field effects Ultrafast phenomena

Atomic, Molecular & Optical

Authors & Affiliations

Markus Ludwig¹, Andrey K. Kazansky ^2,3, Garikoitz Aguirregabiria⁴, Dana Codruta Marinica⁵, Matthias Falk¹, Alfred Leitenstorfer¹, Daniele Brida^1,6, Javier Aizpurua^2,4, and Andrei G. Borisov ^5,*

¹Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457 Konstanz, Germany
²Donostia International Physics Center DIPC, Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián, Spain
³IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain
⁴Material Physics Center CSIC-UPV/EHU, Paseo Manuel de Lardizabal 5, 20018 Donostia-San Sebastián, Spain
⁵Université Paris-Saclay, CNRS, Institut des Sciences Moléculaires d'Orsay, 91405 Orsay, France
⁶Department of Physics and Materials Science, University of Luxembourg, 162a avenue de la Faïencerie, L-1511 Luxembourg, Luxembourg

^*andrei.borissov@u-psud.fr

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Issue

Vol. 101, Iss. 24 — 15 June 2020

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Images

Figure 1
Conceptual sketch of the system. (a) Induced charge density (red, positive; blue, negative) associated with the bonding dipolar plasmon mode of the bowtie nanoantenna embedded in a macroscopic circuit (height $h = 20$ nm and lateral size $L = 360$ nm). Results are obtained from the solution of the classical Maxwell equations for the mode frequency $ω_{0} = 0.68$ eV. (b) Scanning electron micrography (SEM) of the actual experimental device. The red, $E_{g}$ , and white, $J$ , arrows show the direction of the instantaneous electric field and electron current in the gap, respectively. (c) Zoom of panel (a) into the gap region. The size of the gap $d_{g} = 6$ nm and the curvature radii of metal tips $R_{c} = 5$ nm are obtained from analysis of the SEM images. (d) Theoretical model: system of parallel metallic cylindrical nanowires in vacuum ( $R_{c} = 5$ nm; $d_{g} = 6$ nm). The incident single-cycle laser pulse propagates along the $y$ axis and it is linearly polarized with the electric field along the $x$ axis. $(x = 0, y = 0)$ is set at the center of the gap. The bias $U$ is applied to the left cylinder while the right cylinder is grounded.
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Figure 2
Calculated with TDDFT dc bias control of the strong field emission and electron transport in the gap of the nanowire dimer subjected to a single-cycle optical pulse with carrier frequency (a) $ω = 0.6$ eV, (b) $ω = 0.9$ eV, and (c) $ω = 1.2$ eV. The number of electrons transferred between the cylinders per optical pulse and per unit height is shown as a function of the CEP for different applied bias $U$ as explained in the inset.
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Figure 3
Electron transport dynamics in the gap for the incident pulse with carrier frequency $ω = 0.9$ eV and $CEP = 0.875 π$ . Panel (a): time dependence of the optical field in the gap $E_{g} (t)$ . Panels (b) and (c): spatiotemporal profile of the electron density current $J$ along the cylinder dimer $x$ axis. The TDDFT results are shown as a function of the $x$ coordinate and time for an applied dc bias $U = 0$ (b) and $U = 8$ eV (c). Red (blue) color is used for positive (negative) values of $J$ . For further details, see insets.
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Figure 4
Coherent control of the electron transport in the gap of the connected bowtie nanoantenna. Panel (a): time dependent electric field. Free-space experimental transient with $CEP = 0.49 π$ (dashed blue line, scaled by $\times 100$ ); $E_{g} (t)$ calculated with classical Maxwell's equations (TDDFT) in the middle of the gap is shown with red (black) line. Panel (b): net electron current (number of electrons transferred per pulse) through the gap of the bowtie for $CEP = 0.49 π$ . Circles: experimental data as a function of the amplitude of the free-space transient $E_{0}$ ; solid (dashed) line TDDFT (SMM) results calculated as a function of the maximum field reached in the gap $E_{gm}$ . The color code indicates the applied bias as explained in the inset. Panels (c),(d),(e): the CEP dependence of the net electron current. Sets of lines of the same color correspond to the results obtained with a fixed applied bias $U$ and varying the intensity of the laser. In experiment (c) $E_{0}$ is varied between 0.1 and 0.62 V/nm in steps of 0.04 V/nm. The theoretical TDDFT (d) and SMM (e) data correspond to $E_{gm} = 8.32, 8.84, 9.36, 9.88, 10.4$ V/nm.
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