Graphene is a remarkable form of carbon, built from a single layer of tightly connected atoms that is only one atom thick. Despite its thinness, it is highly stable and conducts electricity extremely well. Because of these qualities, graphene is considered a "miracle material" and is already being explored for flexible electronic screens, highly sensitive sensors, advanced batteries, and next-generation solar cells.
A new study led by the University of Göttingen, in collaboration with teams in Braunschweig, Bremen, and Fribourg, shows that graphene may be capable of even more. For the first time, scientists have directly observed "Floquet effects" in graphene. This finding settles a long-running scientific question: Floquet engineering, a technique in which light pulses precisely modify the properties of a material, can also function in metallic and semi-metallic quantum materials such as graphene. The research appears in Nature Physics.
Direct Evidence of Floquet States in Graphene
To probe these effects, the team used femtosecond momentum microscopy, a method that allows researchers to capture extremely fast changes in electronic behavior. The graphene samples were illuminated with rapid bursts of light and then examined with a delayed pulse to follow how the electrons responded over ultrashort timescales.
"Our measurements clearly prove that 'Floquet effects' occur in the photoemission spectrum of graphene," says Dr. Marco Merboldt of the University of Göttingen, the study's first author. "This makes it clear that Floquet engineering actually works in these systems -- and the potential of this discovery is huge." Their results demonstrate that Floquet engineering is effective in a wide range of materials. This brings scientists closer to the ability to shape quantum materials with specific characteristics using laser pulses within extremely short intervals.
Light-Controlled Quantum Materials for Future Technologies
Being able to tune materials with such precision could lay the groundwork for future electronics, computers, and highly advanced sensors. Professor Marcel Reutzel, who led the project in Göttingen together with Professor Stefan Mathias, explains: "Our results open up new ways of controlling electronic states in quantum materials with light. This could lead to technologies in which electrons are manipulated in a targeted and controlled manner."
Reutzel continues: "What is particularly exciting is that this also enables us to investigate topological properties. These are special, very stable properties which have great potential for developing reliable quantum computers or new sensors for the future."
This research was supported by the German Research Foundation (DFG) through Göttingen University's Collaborative Research Centre "Control of Energy Conversion at Atomic Scales."
