Scientists discover class of crystals with properties that may prove revolutionary

Intercrystals exhibit newly discovered forms of electronic properties that could pave the way for advancements in more efficient electronic components, quantum computing and environmentally friendly materials, the scientists said.

As described in a report in the science journal Nature Materials, the scientists stacked two ultrathin layers of graphene, each a one-atom-thick sheet of carbon atoms arranged in a hexagonal grid. They twisted them slightly atop a layer of hexagonal boron nitride, a hexagonal crystal made of boron and nitrogen. A subtle misalignment between the layers that formed moiré patterns -- patterns similar to those seen when two fine mesh screens are overlaid -- significantly altered how electrons moved through the material, they found.

"Our discovery opens a new path for material design," said Eva Andrei, Board of Governors Professor in the Department of Physics and Astronomy in the Rutgers School of Arts and Sciences and lead author of the study. "Intercrystals give us a new handle to control electronic behavior using geometry alone, without having to change the material's chemical composition."

By understanding and controlling the unique properties of electrons in intercrystals, scientists can use them to develop technologies such as more efficient transistors and sensors that previously required a more complex mix of materials and processing, the researchers said.

"You can imagine designing an entire electronic circuit where every function -- switching, sensing, signal propagation -- is controlled by tuning geometry at the atomic level," said Jedediah Pixley, an associate professor of physics and a co-author of the study. "Intercrystals could be the building blocks of such future technologies.

"The discovery hinges on a rising technique in modern physics called "twistronics," where layers of materials are contorted at specific angles to create moiré patterns. These configurations significantly alter the behavior of electrons within the substance, leading to properties that aren't found in regular crystals.

The foundational idea was first demonstrated by Andrei and her team in 2009, when they showed that moiré patterns in twisted graphene dramatically reshape its electronic structure. That discovery helped seed the field of twistronics.

Electrons are tiny particles that move around in materials and are responsible for conducting electricity. In regular crystals, which possess a repeating pattern of atoms forming a perfectly arranged grid, the way electrons move is well understood and predictable. If a crystal is rotated or shifted by certain angles or distances, it looks the same because of an intrinsic characteristic known as symmetry.

The researchers found the electronic properties of intercrystals, however, can vary significantly with small changes in their structure. This variability can lead to new and unusual behaviors, such as superconductivity and magnetism, which aren't typically found in regular crystals. Superconducting materials offer the promise of continuously flowing electrical current because they conduct electricity with zero resistance.

Intercrystals could be a part of the new circuitry for low loss electronics and atomic sensors that could play a part in the making of quantum computers and power new forms of consumer technologies, the scientists said.

The materials also offer the prospect of functioning as the basis of more environmentally friendly electronic technologies.

"Because these structures can be made out of abundant, non-toxic elements such as carbon, boron and nitrogen, rather than rare earth elements, they also offer a more sustainable and scalable pathway for future technologies," Andrei said.

Intercrystals aren't only distinct from conventional crystals. They also are different from quasicrystals, a special type of crystal discovered in 1982 with an ordered structure but without the repeating pattern found in regular crystals.

Research team members named their discovery "intercrystals" because they are a mix between crystals and quasicrystals: they have non-repeating patterns like quasicrystals but share symmetries in common with regular crystals.

"The discovery of quasicrystals in the 1980s challenged the old rules about atomic order," Andrei said. "With intercrystals, we go a step further, showing that materials can be engineered to access new phases of matter by exploiting geometric frustration at the smallest scale."

Rutgers researchers are optimistic about the future applications of intercrystals, opening new possibilities for exploring and manipulating the properties of materials at the atomic level.

"This is just the beginning," Pixley said. "We are excited to see where this discovery will lead us and how it will impact technology and science in the years to come."

Other Rutgers researchers who contributed to the study included research associates Xinyuan Lai, Guohong Li and Angela Coe of the Department of Physics and Astronomy.

Scientists from the National Institute for Materials Science in Japan also contributed to the study.