Scientists use ultrafast laser to flip materials into a different electronic state

A burst of invisible light can do more than illuminate a surface. In a new study, Michigan State University researchers used an ultrafast laser to gently jolt atoms in a quantum material, then watched the surface change in real time. The shift lasted only while the laser stayed on, but it was enough to flip the material into a different electronic state, like a tiny switch you can turn on and off.

The work centers on a layered material called tungsten ditelluride, shortened to WTe2. It has drawn attention for its unusual behavior at the smallest scales. Those surprising traits could matter for future devices, from smaller electronics to parts used in next-generation quantum computers.

The team’s approach blended two sides of modern physics. One group built the instrument and ran the experiments. Another group used computer modeling to explain what the atoms were doing and why it changed the material’s behavior.

The heart of the study is a microscope designed to “feel” atoms. Instead of using lenses, the instrument moves an extremely sharp metal tip across a surface and reads electrical signals, like braille. That scanning tunneling microscope can resolve individual atoms on WTe2.

While watching the surface, the researchers aimed a super-fast laser at the tip. The laser created terahertz pulses, a kind of light that oscillates hundreds of trillions of times per second. Those pulses were focused onto the metal tip, where the electric field became much stronger.

That boosted field allowed the team to wiggle the top layer of atoms directly under the tip. The movement was small, but it mattered. The top layer shifted out of alignment with the layers below, like the top sheet in a stack of paper sliding slightly sideways.

While the pulses stayed on, the material’s surface behaved differently. The team saw new electronic properties that were not present when the laser was off. They also captured images of the “on” and “off” states, showing the switch-like behavior they had created.

“This experience has been a reminder of what science is really like because we found materials that are working in ways that we didn’t expect,” said Tyler Cocker, an associate professor in the College of Natural Science. “Now, we want to look at something that is going to be technologically interesting for people in the future.”

If the motion sounds tiny, it is. The theoretical work helped reveal just how small. Computer simulations found that WTe2 layers shift by about 7 picometers during the laser-driven motion. A picometer is a trillionth of a meter. This is a change so subtle that the microscope alone struggles to measure it cleanly.

Yet in quantum materials, a slight rearrangement can reshape how electrons move. That is the point of a nanoscale switch. You are not forcing a big mechanical change. You are nudging atoms just enough to redirect the rules that electrons follow.

The researchers describe the effect as localized. Only the topmost layer moved in the switching process. That detail matters for future device ideas. A change confined to the surface could, in principle, allow dense packing of tiny switching regions without disturbing the whole material.

“The movement only occurs on the topmost layer, so it is very localized,” said Daniel Maldonado-Lopez, a fourth-year graduate student in Jose L. Mendoza-Cortes’ lab. “This can potentially be applied in building faster and smaller electronics.”

The collaboration formed when Cocker and Jose L. Mendoza-Cortes realized they were approaching similar questions from different directions. Cocker’s group built the specialized microscope and observed the switching. Mendoza-Cortes, an assistant professor in the colleges of Engineering and Natural Science, focuses on simulations that model how atoms and electrons behave.

When the modeling results matched the experimental results, the team gained more confidence in the mechanism. The simulations also filled in details that are hard to see directly, including how the atoms wiggle and the frequencies of that motion.

“Our research is complementary; it’s the same observations but through different lenses,” Mendoza-Cortes shared with The Brighter Side of News. “When our model matched the same answers and conclusions they found in their experiments, we have a better picture of what is going on.”

That “better picture” includes both the size of the atomic shift and the pattern of motion. It also supports the idea that the microscope tip and terahertz pulses work together as a controllable tool, not just a one-off trick.

This study sits in a larger push to create electronics that are smaller, faster, and more energy efficient. The parts inside a phone or laptop rely on materials that were chosen because they behave in stable, predictable ways. But researchers are now searching for materials with new kinds of controllable behavior, especially at the smallest scales where future components may operate.

“When you think about your smartphone or your laptop, all of the components that are in there are made out of a material,” said Stefanie Adams, a fourth-year graduate student in Cocker’s lab. “At some point, someone decided that’s the material we’re going use.”

The new work suggests a different kind of decision could be coming. Instead of selecting a material only for its default behavior, engineers might one day choose a material that can be “re-tuned” on demand, even if only in tiny regions, and even if only for brief moments.

The researchers hope the approach can help drive lower costs, faster speeds, and better energy use in future technology. Their study also points toward potential building blocks for quantum computing, where unusual electronic behavior is often a feature, not a problem.

The research was supported in part through computational resources and services provided by the Institute for Cyber-Enabled Research at Michigan State University.

This work gives scientists a new way to control quantum materials with extreme precision. By using terahertz light focused through a microscope tip, researchers can temporarily switch a material’s surface into a different electronic state and watch the atoms move during the change. That combination of control and visibility can speed up research into other materials with surprising properties, because it links what you see at the atomic level to what the material does electrically.

In the long run, the approach could help guide designs for smaller and faster electronics. A switch that operates through tiny, localized atomic shifts could reduce the size of key components and lower energy demands. The same kind of control may also support progress in quantum computing materials, where engineers need reliable ways to tune electronic behavior without damaging delicate structures.

Even before products appear, the method can help researchers screen new materials faster and understand which atomic motions lead to useful performance.

Research findings are available online in the journal Nature Photonics.

Like these kind of feel good stories? Get The Brighter Side of News' newsletter.