Negative transit time in non-tunneling electron transmission through graphene multilayers

TL;DR

This study uses ab initio scattering theory to analyze electron transmission through graphene multilayers, revealing negative transit times and resonance effects that could impact wave packet control.

Contribution

It uncovers for the first time negative transit times due to in-plane scattering in graphene monolayers and explores the divergence of Wigner time delay at scattering resonances.

Findings

Negative transit time observed in graphene, h-BN, and oxygen monolayers.

Wigner time delay diverges at scattering resonances.

Transit time saturation and oscillations linked to band structure.

Abstract

Attosecond dynamics of electron transmission through atomically-thin crystalline films is studied with an {\em ab initio} scattering theory. The temporal character of the electron propagation through graphene multilayers is traced to the band structure of bulk graphite: In the forbidden gaps the wave packet transit time $\tau_\mathrm{T}$ saturates with thickness and in the allowed bands $\tau_\mathrm{T}$ oscillates following transmission resonances. Hitherto unknown negative transit time due to in-plane scattering is discovered in monolayers of graphene, h-BN, and oxygen. Moreover, Wigner time delay is found to diverge at the scattering resonances caused by the emergence of secondary diffracted beams. This offers a way to manipulate the propagation timing of the wave packet without sacrificing the transmitted intensity. The spatial reshaping of the wave packet at the resonances may help elucidate details of the streaking by an inhomogeneous field at the surface.