Quasiclassical theory of non-adiabatic tunneling in nanocontacts induced by phase-controlled ultrashort light pulses

TL;DR

This paper develops a time-dependent quasiclassical theory to analyze non-adiabatic tunneling in nanogaps driven by ultrashort light pulses, revealing how pulse phase controls electron transport direction and tunneling probabilities.

Contribution

It introduces a novel quasiclassical approach for non-adiabatic tunneling in nanogaps and demonstrates phase-controlled electron transport with analytical expressions.

Findings

Tunneling probability depends exponentially on field strength and contact distance.

Electron transport direction can be controlled by pulse carrier-envelope phase.

Temporal shifts of electron trajectories depend on pulse phase and non-adiabatic effects.

Abstract

We theoretically investigate tunneling through free-space or dielectric nanogaps between metallic nanocontacts driven by ultrashort ultrabroadband light pulses. For this purpose we develop a time-dependent quasiclassical theory being especially suitable to describe the tunneling process in the non-adiabatic regime, when this process can be significantly influenced by the photon absorption as the electron moves in the classically forbidden region. Firstly, the case of driving by an ideal half-cycle pulse is studied. For different distances between the contacts, we analyze the main solutions having the form of a quasiclassical wave packet of the tunneling electron and an evanescent wave of the electron density. For each of these solutions the resulting tunneling probability is determined with the exponential accuracy inherent to the method. We identify a crossover between two tunneling regimes corresponding to both solutions in dependence on the field strength and intercontact distance that can be observed in the corresponding behaviour of the tunneling probability. Secondly, considering realistic temporal profiles of few-femtosecond pulses, we demonstrate that the preferred direction of the electron transport through the nanogap can be controlled by changing the carrier-envelope phase of the pulse, in agreement with recent experimental findings and numerical simulations. We find analytical expressions for the tunneling probability, determining the resulting charge transfer in dependence on the pulse parameters. Further, we determine temporal shifts of the outgoing electron trajectories with respect to the peaks of the laser field in dependence on the pulse phase and illustrate when the non-adiabatical character of the tunneling process is particularly important.