‘Twisted’ 2D materials exhibit unexpected electronic behavior that defies theoretical predictions

In search of new materials that will enable more efficient electronics, scientists are researching so-called 2D materials. These are sheets just one atom thick and can have all sorts of interesting electronic properties. When two sheets are placed on top of each other at a specific angle, new properties such as superconductivity may be created. Materials scientist Antonija Grubisic-Czabo from the University of Groningen and colleagues studied such “twisted” materials and found that they defied theoretical predictions.

The study is published in the journal Physical Review Materials.

Grubisic-Czabo and her team, along with colleagues in Poland, Germany, France, and Italy, studied sheets of a 2D material called tungsten disulfide. Theoretical predictions suggest that when two sheets (called a bilayer) are stacked at an angle of 4.4 degrees, the electrons in the material should exhibit collective behavior.

“And when they are very closely linked, their collective behavior can create new and fascinating effects,” says Giovanna Feraco, lead author of the study.

However, she did not observe this collective behavior in her experiments, which could be explained by interactions between atoms within the bilayer. Twists typically enable these interactions.

“However, by studying the electronic structure of the bilayer, we found that this material tends to ‘relax’ into a region without large twists,” Ferraco explains. Technically speaking, the twisted bilayer partially reverts to a lower energy untwisted configuration.

This finding highlights the importance of understanding how the two sheets of a bilayer form distinct regions with different properties. This work also strengthens scientists’ ability to predict and manipulate the behavior of 2D structures, paving the way for future applications in various types of electronics.