Researchers at ETH Zurich have come up with an exciting new method to control how electrons move in materials. This is done using a special type of structure called moiré materials, which form when very thin layers of atoms are twisted slightly. These artificial crystal lattices can change how electrons behave in a nearby semiconductor without changing the semiconductor itself.
Electrons are vital because they largely determine a material’s electrical and magnetic qualities. However, their interactions are often weak and hard to see. To make these interactions more visible, scientists have been creating larger artificial crystal lattices. This increases the spaces between the electrons and slows them down, which makes their interactions easier to detect.
Traditionally, researchers used moiré materials to enhance these effects, but they also caused unwanted changes in the material. The new ETH Zurich method cleverly uses moiré materials at a distance to create an electric field that influences electrons in a separate layer of semiconductor material, avoiding those complications.
The research, led by Ataç Imamoğlu, focused on two layers of hexagonal boron nitride (h-BN), a very hard substance. By twisting these layers by just under two degrees, they generated a consistent electric field that extended into space around the material.
Below this setup, the team placed a thin layer of molybdenum diselenide (MoSe₂), a semiconductor famous for its unique electronic features. The electric field created by the h-BN layers prompted the electrons in MoSe₂ to arrange themselves into a new, organized structure. This setup allows researchers to examine the behavior of electrons without the interference of additional physical changes.
To see how these electrons arranged themselves, the team used excitons. Excitons are pairs of electrons and empty spots (holes) that form when light hits a material. Because excitons carry no electrical charge, they are unaffected by the electric field, making them perfect for investigating electron dynamics.
By varying the electric voltage applied to the semiconductor, the researchers could control the number of electrons in the lattice. They observed interesting patterns when either one-third or two-thirds of the lattice sites were filled.
This discovery is significant for understanding high-temperature superconductors, which can carry electricity without any resistance. The new technique could help uncover how insulating materials become superconductors when extra electrons are added.
Beyond superconductivity, this approach paves the way for exploring how electrons interact in various quantum materials. By fine-tuning the electric field’s strength, scientists have the chance to probe unique states of matter, like chiral spin liquids, something not yet observed in experiments.
