Subcycle videography of lightwave-driven Landau-Zener-Majorana transitions in graphene

TL;DR

This paper introduces a method for visualizing lightwave-driven electron dynamics in graphene across the entire Brillouin zone with attosecond precision, revealing fundamental quantum tunneling processes and electron scattering effects.

Contribution

It presents the first subcycle, full-zone videography of electron motion in quantum materials, specifically visualizing Landau-Zener-Majorana tunneling in graphene.

Findings

Visualization of non-adiabatic tunneling across the Brillouin zone.

Disentangling of scattering processes affecting electron dynamics.

Observation of coherent electron displacement and distortion in momentum space.

Abstract

Strong light fields have unlocked previously unthinkable possibilities to tailor coherent electron trajectories, engineer band structures and shape emergent phases of matter all-optically. Unravelling the underlying quantum mechanisms requires a visualisation of the lightwave-driven electron motion directly in the band structure. While photoelectron momentum microscopy has imaged optically excited electrons averaged over many cycles of light, actual subcycle band-structure videography has been limited to small electron momenta. Yet lightwave-driven elementary processes in quantum materials often occur throughout momentum space. Here, we introduce attosecond-precision, subcycle band-structure videography covering the entire first Brillouin zone (BZ) and visualize one of the most fundamental but notoriously elusive strong-field processes: non-adiabatic Landau-Zener-Majorana (LZM) tunnelling. The interplay of field-driven acceleration within the Dirac-like band structure of graphene and periodic LZM interband tunnelling manifest in a coherent displacement and distortion of the momentum distribution at the BZ edge. The extremely non-thermal electron distributions also allow us to disentangle competing scattering processes and assess their impact on coherent electronic control through electron redistribution and thermalization. Our panoramic view of strong-field-driven electron motion in quantum materials lays the foundation for a microscopic understanding of some of the most discussed light-driven phenomena in condensed matter physics.