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

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.

Onset of space-charge effects in strong-field photocurrents from nanometric needle tips

“…Our measurements indicate that charge interaction starts to affect the electron dynamics above a near-field intensity of 7.5 × 10 13 W/cm 2 or around 1000 e − /shot for 4.5 fs pulses at 750 nm and tungsten needle tips with a tip radius of around 40 nm. While the strong-field tunneling photocurrent experiments on nano-bowties and triangles [25,28,29,31,48] focus mainly on the CEP-dependent current which is on the order of one electron per shot, the total number of charges per shot is typically several orders of magnitude higher [26,27,31] and therefore in a similar regime as for our experiment. Our study also shows that despite the clear charge interaction, waveform-dependent photocurrents can be measured, which is important for the development of applications of field-controlled currents.…”

Calibrating quantum hydrodynamic model for noble metals in nanoplasmonics

“…Using the optimal model parameters, the QHDM and TD-DFT data largely agree with each other in the overall range of ±0.15 eV. The reliable QHDM response calculations for the above situations would facilitate novel applications of quantum plasmonics in optoelectronics [55][56][57].…”

Impact of DC bias on Weak Optical-Field-Driven Electron Emission in Nano-Vacuum-Gap Detectors

“…The latter case may be preferred in cases where large effective surface areas are desired for increased signal generation. In all cases, when the gap is very small, the preferential emission direction is dictated by the applied bias [12]. The emitter would ideally be fabricated from a plasmonic material, such as gold, enabling large optical field enhancements.…”

“…Due to the high non-linearity of cold-field electron tunneling with respect to the local field outside a material surface, we find that applying a small DC bias between the anode and cathode of the nanoantennas can dramatically increase the probability of emission of a photoelectron from the surface for weak incident optical field strengths (see below where we show a predicted increase of more than 3 orders of magnitude for incident optical field strengths on the order of 10 −4 − 10 1 V nm −1 ). Previous studies have investigated the effect of superimposed electric fields from optical and low-frequency electrical sources in different regimes and length scales [11,12,14]. However, in this work, we investigate the effect of such a combination of optical and DC bias fields at the nanoscale in the weak-field (sub 10 V nm −1 ) ultrafast (sub 100 fs) regime, which has received increasing attention in recent years given the rapid development of nanometer-scale fabrication processes and compact ultrafast optical sources [1,[15][16][17].…”