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Researchers have directly observed Floquet effects in graphene for the first time, settling a long-running scientific debate.
Their ultrafast light-based technique demonstrates that graphene's electronic properties can be tuned almost instantaneously. This paves the way for custom-engineered quantum materials and new approaches in electronics and sensing. 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 Gottingen, 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 semimetallic 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 behaviour. 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," said Marco Merboldt of the University of Gottingen, 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," added Dr Marco. 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 Gottingen together with Professor Stefan Mathias, explained, "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." "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," Reutzel added. This research was supported by the German Research Foundation (DFG) through Gottingen University's Collaborative Research Centre "Control of Energy Conversion at Atomic Scales". (ANI)
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