Suchergebnisse

We report on the theoretical study of the second and third harmonic generation in plasmonic dimer nanoantennas with narrow gaps. Our study is based on the time dependent density functional theory. This allows us to address the nonlinear response of a tunneling junction in a subnanometric plasmonic gaps with a quantum calculation, which goes beyond conventional classical local and nonlocal treatments. We demonstrate that the nonlinear electron transport in a plasmonic junction, associated to the corresponding strong field enhancement in the narrow gap, allows to reach orders of magnitude enhancement in the efficiency of the second and third harmonic generation. Depending on the size of the junction and the frequency of the fundamental incident wave, we show that the frequency conversion in plasmonic dimer gaps can be determined by (i) the intrinsic nonlinearity of each individual nanoparticle, (ii) the nonlinear ac tunneling current across the gap, and (iii) the resonant excitations of the plasmon modes of the dimer. The study of the nonlinear response of plasmonic gaps within a full quantum treatment allows us to understand the fundamental mechanisms of nonlinearity in nanoplasmonics. ; G.A., R.E., and J.A. acknowledge the projects FIS2016-80174-P from Spanish MINECO, project 70NANB15H32 from U.S. Department of Commerce, National Institute of Standards and Technology. G.A., R.E., and A.K.K. acknowledge project PI2017-30 of the Department of Education of the Basque Government. ; Peer reviewed

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. ; The support from the Department of Education of the Basque Government through Project No. PI2017-30 (J.A., A.K.K., and G.A.) and Project No. IT1164-19 for con solidated groups (J.A.) is gratefully acknowledged. A.K.K. acknowledges support from Project No. FIS2016-76617- P of the Spanish Ministry of Economy and Competitiveness. D.B. and A.L. acknowledge support of the Deutsche Forschungsgemeinschaft through the Emmy Noether programme (No. BR 5030/1-1) and the collaborative research center SFB 767. D.B. acknowledges the support by the European Research Council through Grant No. 819871 (UpTEMPO). ; Peer reviewed