Electrons Cross 'Forbidden' Gaps at 100% Probability in Graphene

Electrons in graphene jumped across forbidden energy gaps with a transition probability that reached 100 percent when researchers at the University of Regensburg, Philipps-Universität Marburg and Forschungszentrum Jülich drove them with intense light pulses. The team published the results in Nature on November 13, 2026, and the footage came from a technique they call subcycle videography.

The phenomenon carries a long name: Landau-Zener-Majorana transitions. Physicists have suspected for years that these transitions matter for high-speed semiconductor electronics. Watching one unfold, though, was another matter entirely.

Think of an elevator. You step in on floor one. The display skips "2," "3," "4" — every number up to nineteen — and lands on "20." In everyday life that's absurd. In the quantum world, electrons do it all the time. They cross a forbidden energy gap and land in a different band without ever occupying the states in between.

What did the researchers actually build?

The instrument at the heart of the experiment is a photoemission momentum microscope. It doesn't magnify a surface the way a traditional microscope does. It measures electron energies and momenta directly, letting the team map how electrons distribute themselves across energy states as a light field shoves them around.

Combine that with advanced laser technology and electron microscopy, and you get a slow-motion camera for particles moving on timescales far too short for conventional imaging.

"If you want to know who has won a race, you have to watch all participants," explains Vincent Eggers, first author of the study. "Likewise, we must observe as many electrons as possible at one time to catch those that undergo a quantum mechanical transition while moving."

The technical obstacle was brutal. The team had to drive electrons with light fields oscillating extremely fast while simultaneously recording how their energies and trajectories changed.

"Our team worked on this experiment for many years," says Rupert Huber. "Now, we can track electrons moving across the entire energy landscape of a solid in real time."

Collaborator Ulrich Höfer, a pioneer in ultrafast electron spectroscopy, described the moment it worked: "Being able to observe such a fundamental quantum mechanical process during our first measurement campaign was a very special moment for us — it was also made possible by the samples we used."

Why did the samples matter so much?

The graphene came from Forschungszentrum Jülich. Each carbon layer was one atom thick and had to be nearly flawless, because impurities would obscure the delicate quantum dynamics under observation.

"These precision experiments require material that is nearly perfect at the atomic level," emphasizes Stefan Tautz of Forschungszentrum Jülich. He also credits "rotated" graphene — a Jülich specialty — with making the quantum dynamics emerge particularly clearly.

How is this different from tunneling?

The 100 percent figure highlights what makes Landau-Zener-Majorana transitions so strange. Electrons hop between states separated by a substantial energy gap, and they do it with near-certainty. The crucial variable is how quickly the electric field sweeps the electrons toward the gap. That distinguishes the process from conventional quantum tunneling, where particles pass through a barrier in physical space.

What comes next?

Beyond confirming a fundamental effect, the imaging technique revealed why electrons lose their orderly motion: interactions with graphene's crystal lattice gradually disrupt it. That insight matters for future electronics that would steer electrons with the ultrafast oscillations of light rather than electrical voltages alone.

The researchers expect the method to transfer to many other quantum materials. Giacomo Inzani of the University of Regensburg put it plainly: "Our experiment opens a panoramic window into the quantum world. Now, we can follow in real time how electrons move through the energy landscape of a material. And this is just the beginning."

The journal reference is V. Eggers et al., "Subcycle videography of Landau–Zener–Majorana transitions in graphene," Nature 659 (8139): 63, DOI: 10.1038/s41586-026-11214-y. Whether light-controlled electronics moves from lab curiosity to a commercial switching concept will depend on how well researchers tame the lattice interactions that scatter these perfectly obedient electrons.