Laser Pulses Trigger Ultrafast Material Property Shift

Researchers from the Fritz Haber Institute of the Max Planck Society and the Max Planck Institute for the Structure and Dynamics of Matter demonstrated the ability to use light to achieve a novel type of ultrafast switch. The efforts stem from the collaborators’ pursuit of ever-increasing speed in electronics and computing technologies. Transistors that turn electrical currents on and off quickly are pillars of those technologies.

The researchers’ focus was to induce changes in a material’s properties, such as making magnetic materials nonmagnetic or changing the electric conductivity of a crystal. Electrical properties of a material relate strongly to the arrangement of the electrons within the crystal. As such, control of the arrangement of electrons within a material has been a research pursuit for decades, though methods thus far have been fairly slow.

A femtosecond burst of light drives an exotic electronic transition in a semimetallic crystal, on an unprecedently fast timescale. Courtesy of Samuel Beaulieu.

“We knew that external influences like temperature or pressure variations work, but that takes time, at least a few seconds,” said Ralph Ernstorfer, group leader at the Department of Physical Chemistry at the Fritz Haber Institute.

The team turned to light to increase the speed.

Using new equipment at the Fritz Haber Institute, the researchers cut down the switching time to only 100 femtoseconds. To do this, they fired ultrashort laser pulses at a semimetallic crystal composed of tungsten and tellurium atoms. Light shined on the crystal encouraged it to reorganize its electronic structure, which also changed its conductivity. Additionally, the scientists were able to observe exactly how the electronic structure changed.

“We used a new instrument to take pictures of the transition every step of the way,” said Samuel Beaulieu, who worked as a postdoctoral fellow with Ernstorfer. “This is amazing progress — we used to only know what the electronic structure of the material looked like after, but never during the transition.”

Researchers at the Max Planck Institute for the Structure and Dynamics of Matter also acquired details on how the transition occurs, and, more specifically, how it begins. The laser pulse impinging on the materials changes the way electrons interact with each other. This type of transition is known as a Lifshitz transition.

The researchers expect that the method will generate further study into possible transistor materials.

The research was published in Science Advances (www.doi.org/10.1126/sciadv.abd9275).