Bergholtz is driven by curiosity and a determination to constantly develop himself and his knowledge.

“It’s difficult to innovate as a researcher if you restrict yourself to one and the same field. What’s more, tackling new disciplines offers a number of advantages. You’re not burdened by preconceived notions or detailed knowledge that can create obstacles,” says Bergholtz, professor of theoretical physics at Stockholm University.

Unusual material properties

The pursuit of renewal is also behind Bergholtz’s research breakthrough. Topological systems are the primary focus of his research​​. This is an area of physics in which mathematical tools are used to explore and explain unusual states of matter.

One breakthrough came when knowledge from a related field was found to increase the understanding of open topological systems, which are systems that interact with their surroundings. The theories that Bergholtz developed together with his research team laid the foundations for a completely new field of research with a new theoretical framework.

“Initially, our ideas met with a lot of criticism, but now the field is well established both experimentally and theoretically. Early on, we also thought about building a new kind of sensor based on our results. Today, several international research groups have built such sensors.”

But the sensors built elsewhere do not take full advantage of underlying theories. This led the research group to set up a lab in AlbaNova (the Stockholm Center for Physics, Astronomy and Biotechnology) to build its own sensor.

“We’re building an optical version of the sensor taking inspiration from researchers at the California Institute of Technology. They apparently missed a key aspect, which among other things, renders the sensor unscalable. Now I’m looking forward to learning more about the whole process from abstract theory to an actual application.”

Nothing to measure?

The sensor will make it possible to measure very weak signals, such as extreme resistance in a material. But the sensor does not yet have any practical applications.

“It’s a common theme of basic research: not knowing what results can be used for. Admittedly, there are dreams of measuring signals from dark matter and so on. But we’re getting started by investigating whether it can be built at all.”

If you want to learn about modern physics, for example quantum physics, you need to put your previous knowledge to one side. You need to find a new way of thinking; it’s a bit like becoming a child again.

Meanwhile, Bergholtz has taken on another project in an adjacent field: investigating topological phases in new forms of semiconductors and semimetals, so-called van der Waals materials. These consist of thin layers that give them unique electrical, optical and mechanical properties, especially when twisted. One such material is graphene.

“We have extensive experience of this type of physics from before, although on a more conceptual level. Now new types of van der Waals materials are being developed that fit the theories we developed more than ten years ago.”

The hope is that the research group’s work will provide valuable insights to researchers who develop and experiment with these new materials. As recently as 2020, the research group published a scientific article on topological phases in these materials.

“Back then, our focus was on graphene, but now there are so many more alternatives. The new materials make it possible to achieve special quantum states without strong magnetic fields or extremely low temperatures, thereby raising hopes of a number of different applications in the future, including in quantum computers.”

As both projects concern the field of topology, there are obvious synergies between the two, Bergholtz believes. In addition, moving between the two projects spurs new ideas.

“The key to success for our group has been to move between different fields. We share knowledge and inspiration between them, which makes it possible to tackle entirely new things.”

Sharing knowledge

To move the research forward, international collaboration is important, but even more crucial is the Arxiv.org website, which serves as a publication platform for scientific articles that have not yet been accepted for publication. When it was founded in 1991, it focused on physics, but today it contains articles on a range of different subjects. Similar platforms also exist for other subjects, and they are referred to as “preprint servers”. Bergholtz simply calls it the Archive.

“The Archive has meant a great deal to developments in physics as well as mathematics. It’s invaluable to us because it provides immediate access to new ideas. It also brings together everything under the same roof.”

Arxiv has become part of Bergholtz’s daily routine. Every morning before breakfast, he skims through the latest published research articles on a range of related fields. When he finds something relevant, he shares it with the group so they can discuss the results together throughout the day.

“It would just be impossible to go through scientific journals in the same way. Now I look through about a hundred articles every day. It’s actually become something of a lifestyle for me.”

Text Magnus Trogen Pahlén
Translation Nick Chipperfield
Photo Magnus Bergström