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Laser Pulses Trigger Ultrafast Material Property Shift

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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 semi-metallic crystal, on an unprecedently fast timescale. Courtesy of Samuel Beaulieu.
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).

Photonics Handbook
GLOSSARY
transition
The process whereby a quantum mechanical system alters from one energy level to another. During this process, energy is emitted or absorbed, and it usually takes the form of photons, phonons, or kinetic energy of particles. Transitions concerned with photons alone are called direct radiative transitions, whereas those having a combination of a photon and a phonon are called indirect.
crystal
A solid with a structure that exhibits a basically symmetrical and geometrical arrangement. A crystal may already possess this structure, or it may acquire it through mechanical means. More than 50 chemical substances are important to the optical industry in crystal form. Large single crystals often are used because of their transparency in different spectral regions. However, as some single crystals are very brittle and liable to split under strain, attempts have been made to grind them very...
electron
A charged elementary particle of an atom; the term is most commonly used in reference to the negatively charged particle called a negatron. Its mass at rest is me = 9.109558 x 10-31 kg, its charge is 1.6021917 x 10-19 C, and its spin quantum number is 1/2. Its positive counterpart is called a positron, and possesses the same characteristics, except for the reversal of the charge.
Research & TechnologylasersmaterialstransitionpropertycrystalelectronMax PlanckMax Planck Institute for the Structure and Dynamics of MatterFritz Haber InstituteMax Planck Societyelectricelectrical propertiesLifshitzScience AdvancesEurope

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