Weyl you were working

In 2011, theoretical physicist Anton Burkov was researching how magnetic fields affected a group of materials known as “topological insulators.” Such materials don’t conduct electricity internally, but can do so along their surface. They’re a type of “quantum material,” a larger category that includes materials exhibiting all kinds of unusual properties.

At a major conference on condensed-matter physics that year, he attended a talk about another, even more exotic category of quantum materials known as “Weyl semimetals,” which are as scientifically intriguing as they are difficult to create.

“[During that talk] I saw a picture that looked very similar to the pictures I’d generated when I did this work on surface states of topological insulators,” Burkov said. “That’s how I got an idea of how to make a Weyl semimetal that was much simpler.”

Weyl semimetals’ precise and highly sensitive electronic structure makes them difficult to produce and easy to destroy. Their unusual properties, though, make them both scientifically interesting, and also potentially valuable for commercial and industrial purposes.

Burkov, an Associate Faculty researcher in quantum materials at Perimeter and a Professor at the University of Waterloo, collaborated with his former postdoctoral advisor on a paper outlining how it might be possible to create a particularly simple realization of such materials (in theory, the simplest possible), not hampered by messy details in other proposals.

“This was the quickest paper I’ve ever written. It only took a couple of weeks because it was a very, very simple idea,” he said.

That simple idea took nearly 15 years to confirm experimentally. The theory remained a theory from 2011 until 2025, when a team of researchers at the RIKEN Institute in Japan created the world’s first ideal Weyl semimetal — using the very method Burkov had proposed.

More familiar states of matter like solids, liquids, and gases are defined by properties like whether they have a defined shape and/or volume. Weyl semimetals and other such materials are instead distinguished by their quantum properties, notably including if and how they conduct electricity (including superconductivity), react to magnetic fields, and so on. Weyl materials are of particular interest to theoretical physicists, as they contribute to research areas like quantum field theory and the Standard Model, which classifies all the known elementary particles — the building blocks of reality.

In addition to their theoretical value, Weyl semimetals could have major practical applications if researchers can find easier ways to produce them: they exhibit a phenomenon called quantum anomalous Hall effect, which could make them useful for low-power electronic devices. Their unusual reaction to magnetic fields also makes them valuable as components in high-tech sensors, and their “optoelectronic” properties can make them useful for generation and detection of terahertz radiation.

Burkov never doubted his theory was correct, but knew that experimental confirmation would be difficult. Weyl semimetals get their properties from pairs of “quasiparticles,” which arise from quantum interactions and have opposite chirality or handedness. If they collide, the pairs annihilate one another, but if they retain a gap between them, they are essentially indestructible.

Even when these quasiparticle pairs can be maintained, though, their desirable properties can be obscured by other electronic states in the same material. The challenge for the RIKEN group was to create a material with pairs of these massless “Weyl fermions,” without interference from other electronic states. They published their results in Nature in early 2025.

Though the RIKEN group had worked on the problem for more than four years, Burkov only heard about their project when they posted a draft of their paper to the preprint website ArXiv.

“This was a surprise to me. Even though this idea theoretically was very simple, the thinking was that realising it experimentally would be extremely difficult. For that reason, people have basically not seriously tried even to take that route,” he said.

He says that while the RIKEN group’s success represents a major advance, his model still suggests these materials could get even better, making their desirable qualities more distinct and pronounced. There are still issues with “magnetic impurities” that create disorder in the existing realizations.

“What needs to be done is basically making these materials cleaner in order to really make the effects spectacular and also useful. This current material is not quite there yet,” he said.

Still, he said, there was professional satisfaction in seeing his theory confirmed in the lab after so many years.

“This made my day,” he said. “I was happy.”