Researchers at ETH Zurich have developed a groundbreaking technique to manipulate electrons within materials using artificial crystal lattices. By leveraging moiré materials, created by twisting ultra-thin atomic layers, they have found a way to influence electron behavior in a nearby semiconductor without directly altering its physical properties.
A Fresh Perspective On Electrons Interactions
Electrons play a crucial role in determining a material’s electrical and magnetic properties. However, their interactions are typically weak and difficult to observe. To amplify these effects, scientists create artificial crystal lattices with larger lattice constants, which increases the spacing between electrons and reduces their motion. This method makes their interactions more noticeable.
In the past, moiré materials—structures formed by stacking and slightly misaligning atomic layers—were used to achieve this. While effective, these materials also introduce unwanted physical changes, complicating the study of electron interactions.
The new approach developed by ETH Zurich circumvents this issue by using moiré materials remotely to generate an electric field that influences electrons in a separate semiconductor layer.
Twisting Boron Nitride To Reshape Electron Behavior
The research team, led by Ataç Imamoğlu, utilized two layers of hexagonal boron nitride (h-BN), a material nearly as hard as diamond. By twisting these layers by less than two degrees, they created a periodic electric field that extended beyond the material.
Below this moiré structure, they placed a thin layer of molybdenum diselenide (MoSe₂), a semiconductor known for its unique electronic properties.
This electric field influenced the electrons in the MoSe₂, forcing them to organize into an artificial crystal lattice. Unlike conventional moiré materials, this setup allows scientists to study electron behavior in a more controlled and isolated environment, free from additional physical alterations.
Using Excitons to Probe Electron Patterns
To observe how electrons arrange themselves in this artificial lattice, the researchers used excitons—pairs of electrons and holes that form when a material absorbs light of a specific wavelength. Because excitons are electrically neutral, they remain unaffected by the periodic electric field, making them an ideal probe for studying electron dynamics.
By adjusting the electric voltage applied to the semiconductor, the scientists controlled the number of electrons filling the lattice sites. They found that when either one-third or two-thirds of the sites were occupied, the electrons self-organized into regular patterns.
Unlocking the Mysteries of Superconductivity
Understanding electron interactions is a key step in unlocking the potential of high-temperature superconductors—materials that conduct electricity without resistance. This new method could provide deeper insights into how insulating materials transition into superconducting states when additional electrons are introduced.
Beyond superconductivity, the highly controllable nature of this technique opens new avenues for exploring electron interactions in other quantum materials. By adjusting the strength of the electric field, researchers could investigate exotic states of matter such as chiral spin liquids, a phenomenon that has never been observed experimentally.
