Team of Researchers from the Technion and Germany Demonstrates Optical Control of Electrons in an Out-of-Equilibrium Topological State
A study published in Nature Physics reports an unprecedented achievement by researchers from the Technion and Germany: using laser light to control electrons inside light-dressed graphene. The study’s lead researchers are Dr. Ofer Neufeld of the Technion’s Schulich Faculty of Chemistry and Helen Diller Quantum Center, and his colleagues in Germany, Prof. Peter Hommelhoff and Dr. Daniel Lesko.
For the first time, researchers have demonstrated direct control of electrons in a “Floquet topological insulator,” a temporary quantum state created by exposing graphene to ultrashort laser pulses. Graphene is a single layer of carbon atoms arranged in a honeycomb pattern. While it may resemble an extremely thin form of graphite, the material found in pencil lead, its properties are strikingly different. It is several times stronger than a steel sheet of comparable thickness, nearly transparent, and highly conductive.
In their Nature Physics paper, the researchers show that precisely timed laser pulses can temporarily transform graphene’s properties, creating a new quantum state known as a Floquet topological insulator. Additional light pulses can then be used to control the movement of electrons within this transient phase of matter.
The achievement is particularly significant because it demonstrates active control of electrons in an out-of-equilibrium topological state for the first time. It provides experimental evidence for ideas developed in recent years about quantum materials and how light can alter their properties. In particular, the researchers showed that this quantum state produces chiral responses: the electric current generated in the material behaves differently when illuminated with light whose polarization rotates clockwise or counterclockwise. By mapping the resulting currents against the polarization and timing of the laser pulses, they revealed the quantum state’s sensitivity to phase. This finding could lead to new ways of measuring out-of-equilibrium material properties.
Dr. Neufeld led the theoretical work, while his colleagues in Germany led the experiments. A Technion alumnus, Dr. Neufeld recently returned as a faculty member after completing postdoctoral research at the Max Planck Institute in Hamburg.
“The implications of this research extend beyond graphene,” said Dr. Neufeld. “We believe our findings could help enable faster, more energy-efficient electronic components, as well as communications, sensing, and computing systems based on properties that can be switched on and off with light.”
The research was supported by the German Research Foundation (DFG), the European Union’s FET Open program under Horizon 2020, and the Gordon and Betty Moore Foundation.
Prof. Peter Hommelhoff and Dr. Daniel Lesko are researchers affiliated with Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU) and Ludwig Maximilian University of Munich (LMU).
About Dr. Ofer Neufeld
Dr. Ofer Neufeld is a theoretical physicist who studies interactions between light and matter on ultrafast timescales, particularly quantum processes that occur under strong laser fields. He completed his bachelor’s, master’s, and doctoral degrees at the Technion before undertaking postdoctoral research in Prof. Angel Rubio’s group at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany. He returned to the Technion in 2024 as a faculty member in the Schulich Faculty of Chemistry.
Read the paper in Nature Physics
