New technique films light-driven quantum tunneling of electrons in graphene

The effect is known as Landau-Zener-Majorana tunneling, in which electrons moving quickly through an avoided crossing in the band structure jump from the valence band to the conduction band. The team says a direct observation of this process in momentum space had been missing. Their method pairs a phase-stable, few-cycle mid-infrared pulse that drives the electrons with an extreme ultraviolet probe pulse, and a photoemission momentum microscope records the energy and momentum of every emitted electron. This allowed them to track the motion across the entire first Brillouin zone, which they say increases the accessible momentum area by more than two orders of magnitude and the usable field strengths by one order of magnitude compared with earlier subcycle photoemission experiments.

Researchers at the University of Regensburg, Philipps University of Marburg, Forschungszentrum Jülich, the Jülich Aachen Research Alliance (JARA) and RWTH Aachen University have directly imaged how the electric field of a light pulse drives electrons across the energy gap in graphene, using a new technique with attosecond precision.The effect is known as Landau-Zener-Majorana tunneling, in which electrons moving quickly through an avoided crossing in the band structure jump from the valence band to the conduction band. The team says a direct observation of this process in momentum space had been missing. Their method pairs a phase-stable, few-cycle mid-infrared pulse that drives the electrons with an extreme ultraviolet probe pulse, and a photoemission momentum microscope records the energy and momentum of every emitted electron. This allowed them to track the motion across the entire first Brillouin zone, which they say increases the accessible momentum area by more than two orders of magnitude and the usable field strengths by one order of magnitude compared with earlier subcycle photoemission experiments.

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