Femtosecond field-driven on-chip unidirectional electronic currents in nonadiabatic tunnelling regime

TL;DR

This paper demonstrates room-temperature, air-operable femtosecond optical pulse to electronic current conversion in plasmonic nanojunctions, revealing ultrafast dynamics and fundamental speed limits of the process.

Contribution

It uncovers the mechanisms of photoemission and ultrafast current dynamics in plasmonic nanojunctions operating at room temperature and in air, advancing on-chip ultrafast electronics.

Findings

Photoemission mechanisms in plasmonic nanojunctions are characterized.

Ultrafast current dynamics are governed by electron wavepacket reshaping.

Electron flight time correlates with ponderomotive velocity in the driving field.

Abstract

Recently, asymmetric plasmonic nanojunctions [Karnetzky et. al., Nature Comm. 2471, 9 (2018)] have shown promise as on-chip electronic devices to convert femtosecond optical pulses to current bursts, with a bandwidth of multi-terahertz scale, although yet at low temperatures and pressures. Such nanoscale devices are of great interest for novel ultrafast electronics and opto-electronic applications. Here, we operate the device in air and at room temperature, revealing the mechanisms of photoemission from plasmonic nanojunctions, and the fundamental limitations on the speed of optical-to-electronic conversion. Inter-cycle interference of coherent electronic wavepackets results in a complex energy electron distribution and birth of multiphoton effects. This energy structure, as well as reshaping of the wavepackets during their propagation from one tip to the other, determine the ultrafast dynamics of the current. We show that, up to some level of approximation, the electron flight time is well-determined by the mean ponderomotive velocity in the driving field.