This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Using a new slow-motion electron camera, physicists from Regensburg, Marburg and Jülich revealed how intense electric fields drive electrons in graphene, causing them to jump across energy gaps in a seemingly paradoxical manner. This was made possible by a novel combination of laser technology and electron microscopy.
The electrons' behavior is roughly equivalent to riding an elevator where the floor indicator suddenly jumps from "1," "2," and "3" to "20." You never passed through the 17 floors in between, yet you arrive on the 20th floor. What sounds like an impossible leap is actually possible in the quantum world. Such processes are called Landau-Zener-Majorana transitions.
It has long been suspected that these transitions could play an increasingly important role in high-speed semiconductor electronics. A research team from the University of Regensburg, Philipps-Universität Marburg and the Forschungszentrum Jülich has succeeded in visualizing the ultrafast dynamics of such transitions in the material graphene. The team reports on this achievement in its latest study, published in the journal Nature.
The researchers observed how electrons are accelerated by the electric field of a light pulse and switch between energy bands as they move. In semiconductors and related materials, electrons can only occupy certain energy ranges, known as bands, which are separated by a forbidden energy gap. Typically, electrons remain firmly trapped in their respective bands.
However, during a Landau-Zener-Majorana transition, electrons appear to overcome this forbidden zone with ease. In order to observe such extremely fast processes, the team developed a novel combination of laser technology and electron microscopy. "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." This is made possible by a so-called photoemission momentum microscope. Unlike a conventional microscope, it does not show magnified images of objects. Instead, it records the energies and states of motion of the electrons and uses them to create a map of their distribution.
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