Materials with unexpected electronic properties found in twisted layers

Researchers at the University of Groningen, in collaboration with international teams, have uncovered surprising electronic behavior in two-dimensional (2-D) materials with a "twist." These ultra-thin materials, consisting of layers just one atom thick, are promising candidates for advanced electronic applications due to their unique properties. When two such layers are stacked at specific angles, theoretical predictions suggest the emergence of phenomena like superconductivity. However, recent experiments defied these predictions.

Antonija Grubisic-Cabo, a materials scientist at the University of Groningen, led a study on bilayer tungsten disulfide - a 2-D material known for its intriguing electronic characteristics. The research aimed to explore how stacking these sheets at a 4.4-degree angle influences electron behavior. Giovanna Feraco, the study's first author, explained that theory suggested this angle would induce collective electron behavior, potentially giving rise to novel electronic effects.

"'And when they are so closely connected, their collective behaviour can create new, fascinating effects,' says Giovanna Feraco, first author of the study."

Contrary to expectations, the experiments revealed no such collective behavior. "'But by studying the electronic structure in the bilayer, we discovered that this material tends to "relax" into large, untwisted regions,' Feraco explains." This structural relaxation partially reverts the bilayer to a lower-energy configuration, which disrupts the predicted interactions between the atoms.

The findings underscore the importance of understanding the structural dynamics of bilayer materials, as these interactions can significantly alter electronic properties. This new insight will refine predictions about 2-D materials and enhance researchers' ability to design and control them for future electronic applications.

Research Report:Nano-ARPES investigation of structural relaxation in small angle twisted bilayer tungsten disulfide