Ultrafast imaging captures graphene electrons crossing energy gaps with up to 100% probability

Scientists in Germany have observed electrons crossing an energy gap in graphene with a probability of up to 100%, revealing how intense electric fields can drive quantum transitions in real time. Researchers from the University of Regensburg, Philipps University of Marburg, and Forschungszentrum Jülich used a new imaging technique combining ultrafast lasers with electron microscopy to track the movement of electrons in the atomically thin material, capturing a process known as Landau-Zener-Majorana transitions, in which electrons move between energy bands without occupying the forbidden energy states separating them.

The measurements showed that electrons could cross the energy gap with a tunneling probability reaching 100% under the experimental conditions, and the result demonstrates that transitions between separated energy states can become highly probable when electrons are driven rapidly enough.

The team used specially prepared, exceptionally pure graphene samples produced at Forschungszentrum Jülich, including rotated graphene structures that made the quantum dynamics easier to observe. Stefan Tautz of Forschungszentrum Jülich said these precision experiments require material that is nearly perfect at the atomic level, ensuring impurities do not obscure the delicate quantum dynamics of the electrons.

The researchers said their approach could also be applied to other quantum materials, allowing scientists to investigate electronic behavior that has previously been difficult to observe directly. The study appears in Nature.