Researchers from the Department of Physical Chemistry at the Fritz Haber Institute and the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg have found that ultra-fast commutations in material properties can be triggered by pulses laser – and why. This knowledge can allow new concepts of transistors.
Maximizing the speed of electronic technology is a central goal of contemporary materials research. The key components of fast computing technologies are transistors: switching devices that turn electrical currents on and off very quickly as basic steps of logic operations. In order to improve our knowledge of ideal transistor materials, physicists are constantly trying to determine new methods for making such extremely fast switches. Researchers at the Fritz Haber Institute of the Max Planck Company in Berlin and the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg have now understood that a new type of ultra-fast switch can be achieved with the light.
Physicists involved in the project are studying how best to cause materials to change their properties – to make metals magnetic non-magnetic, for example, or to change the electrical conductivity of a crystal. The electrical properties of a material are strongly related to the arrangement of electrons in the crystal. The control of the arrangement of electrons has been a key subject for decades. Most control methods, however, are quite slow. “We knew that external influences like changes in temperature or pressure work,” says Dr Ralph Ernstorfer, group leader in the department of physical chemistry at the Fritz Haber Institute, “but it takes time, at least some seconds ”. Those who regularly use a smartphone or computer know that a few seconds can seem like forever. So Dr. Ernstorfer’s group explored how to change the properties of materials much faster using light.
Using brand new equipment from the Fritz Haber Institute, the researchers massively reduced the switching time to just 100 femtoseconds – 0,000,000,000,000 1 of a second – by launching ultrashort optical laser pulses at the chosen material, a semi. metallic. crystal composed of tungsten and tellurium atoms. The bright light on the crystal encourages it to rearrange its internal electronic structure, which also changes the conductivity of the crystal. In addition, scientists were able to observe exactly how its electronic structure changed. “We used a new instrument to take photos of the transition at each step of the process,” explains Dr. Samuel Beaulieu, who worked as a postdoctoral fellow with Ralph Ernstorfer at the Fritz-Haber-Institut (2018-2020) and who is now a permanent researcher at the Center Lasers Intenses et Applications (CELIA) of the CNRS-University of Bordeaux. “This is incredible progress – we only knew what the electronic structure of the material looked like before, but never during the transition,” he adds. Additionally, state-of-the-art modeling of this new process by Dr Nicolas Tancogne-Dejean, Dr Michael Sentef and Prof. Dr Angel Rubio of the Max de Planck Institute for the Structure and Dynamics of Matter has revealed the origin of this new type of ultra-fast electronic transition. The laser pulse hitting the materials changes the way electrons interact with each other. It is the driving force behind this exotic transition, known as the Lifshitz transition.
This method is expected to generate a lot of knowledge on possible future transistor materials. The very fact that light can drive ultra-fast electronic transitions is a first step towards even faster and more efficient technology.
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