Sub-cycle optical phase control of nanotunnelling in the single-electron regime

Abstract

The high peak electric fields provided by single-cycle light pulses can be harnessed to manipulate and control charge motion in solid-state systems, resulting in electron emission out of metals and semiconductors [1][2][3][4][5][6] or high harmonics generation in dielectrics 7,8 . These processes are of a non-perturbative character and require precise reproducibility of the electric-field profile 9-14 . Here, we vary the carrier-envelope phase of 6-fs-long near-infrared pulses with pJ-level energy to control electronic transport in a laterally confined nanoantenna with an 8 nm gap. Peak current densities of 50 MA cm -2 are achieved, corresponding to the transfer of individual electrons in a half-cycle period of 2 fs. The observed behaviours are made possible by the strong distortion of the effective tunnelling barrier due to the extreme electric fields that the nanostructure provides and sustains under sub-cycle optical biasing. Operating at room temperature and in a standard atmosphere, the performed experiments demonstrate a robust class of nanoelectronic switches gated by phase-locked optical transients of minute energy content.Present-day high-frequency devices operate in the microwave range, but direct control of electron flow by the electric-field profile of few-cycle optical pulses has recently been demonstrated 12,15 . These experiments were based on strong perturbation of the electronic system in a dielectric material, resulting in a large incoherent background current. Nanoscale confinement of the region biased by the optical transient might avoid a significant influence of nonlinear conductivity in an insulating substrate and result in purely coherent tunnelling currents 16 that may be controlled by the precise shape of the electric field cycles. Our approach to reaching this goal is illustrated in the upper part of Fig. 1a. A single-cycle near-infrared pulse (left) is focused to a nanoscale junction of an electronic circuit (centre) with nonlinear and antisymmetric current-voltage (I-V) characteristics (right). An effective bias then arises when the exciting electric field is cosine-shaped (blue transient and blue dot in the I-V scheme) because its extremum occurs only for one polarity. Consequently, the symmetry of electronic transport is broken, even when integrating over the entire transient, and a net tunnelling current of electrons results through the potential barrier represented by the free-space gap (Fig. 1b,c). Our experiment favours tunnelling over other phenomena such as multiphoton ionization 4 by operating with ultrashort pulses and extreme nanoconfinement of the electric field. No background current exists when the control field is sineshaped (red transient and dot in the I-V characteristics, respectively), because positive and negative polarities now have precisely opposite effects. Consequently, the total current amplitude and direction may be set by varying the carrier-envelope phase (CEP), Δφ CEP , of the pulse. Owing to the single-cycle pulse duration, nanoscale constriction and fi...

Towards properties on demand in quantum materials

“…An added value of this line of research is that attosecond pulses also enable damage-free exposure of insulating solids to electric fields of the order of the Zener critical field F crit = E g /ea. Ultra-rapid reversible optical waveforms were shown to increase the a.c. conductivity of wide-bandgap dielectrics by more than 18 orders of magnitude within 1 femtosecond 13,122 . These experiments open pathways for signal processing in the petahertz domain, which is not attainable with common electronics.…”

Perspective on Petahertz Electronics and Attosecond Nanoscopy

“…It has been shown that the energyresolved spectra of photo-emitted electrons in the regime close to the cutoff energy are strongly modulated by the CEP, which can be used to retrieve the position-resolved absolute phase of a laser beam [70]. More recently, experiments have shown that the total electron yield from a single junction [105] or from an array of nanostructures [106] is also CEP dependent, see Fig. 3.…”

Sub-Cycle Effects in Carrier-Envelope-Phase-Sensitive Photoemission from Plasmonic Nanoparticles

“…electric fields in the hundreds of terahertz regime, can control electron motion around solid-state nanostructures. Most notably, carrier-envelope-phase-sensitive (CEP-sensitive) effects have been observed in photoemission currents from metallic nano-tips [1,2] and, more recently, from metallic nanoparticles [3,4]. Here, we report measurements of CEP-sensitive photoemission from plasmonic nanoparticles driven by few-cycle laser pulses of variable intensity.…”