In research likely to spark interest in an enigmatic class of materials called quasicrystals, MIT scientists and their colleagues have discovered a relatively simple and flexible way to create new atomically thin versions that can be tailored to special phenomena. important. In work reported in a recent problem of Naturethey describe doing just that to make the materials exhibit superconductivity and much more.
The research introduces a new platform not only for learning more about quasicrystals, but also for exploring exotic phenomena that may be difficult to study but could lead to important applications and new physics. For example, a better understanding of superconductivity, in which electrons pass through a material without resistance, could enable the development of much more efficient electronic devices.
The work brings together two previously unconnected fields: quasicrystals and twistronics. The latter is the specialty of Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT and corresponding author of the new Nature paper, of which Graphene breakthrough “magic angle” in 2018, the domain was relaunched.
“It is truly extraordinary that the field of twistronics continues to make unexpected connections with other areas of physics and chemistry, in this case the beautiful and exotic world of quasiperiodic crystals,” says Jarillo-Herrero , also affiliated with the MIT Materials Research Laboratory and the MIT Electronics Research Laboratory.
Do the twist
Twisttronics involves layers of atomically thin materials placed on top of each other. Rotating or twisting one or more layers at a slight angle creates a unique pattern called a moiré superlattice. And a moiré pattern, in turn, impacts the behavior of electrons. “This changes the spectrum of energy levels available to electrons and can create the right conditions for interesting phenomena to occur,” says Sergio C. de la Barrera, one of the paper’s four co-first authors. recent. De la Barrera, who conducted the work while a postdoctoral fellow at MIT, is now an assistant professor at the University of Toronto.
A moiré system can also be tailored to different behaviors by changing the number of electrons added to the system. As a result, the field of twistronics has exploded over the past five years, as researchers around the world have applied it to creating new atomically thin quantum materials. Examples from MIT alone include:
- Transforming a moiré material known as magic angle twisted bilayer graphene into three different – and useful – electronic devices. (The scientists involved in this work, reported in 2021, included Daniel Rodan-Legrain, co-first author of the current work and a physics postdoctoral fellow at MIT. They were led by Jarillo-Herrero.)
- Engineering a new property, ferroelectricity, in a well-known family of semiconductors. (The scientists involved in this work, reported in 2021were led by Jarillo-Herrero.)
- Predict new exotic magnetic phenomena, with a “recipe” to achieve them. (The scientists involved in this work, reported in 2023, included MIT physics professor Liang Fu and Nisarga Paul, an MIT graduate student in physics. Both Fu and Paul are co-authors of the current paper.)
Towards new quasicrystals
As part of the current work, the researchers were tinkering with a moiré system made up of three sheets of graphene. Graphene is made up of a single layer of carbon atoms arranged in hexagons resembling a honeycomb structure. In this case, the team layered three sheets of graphene, but twisted two of those sheets at slightly different angles.
To their surprise, the system created a quasicrystal, an unusual class of material discovered in the 1980s. As their name suggests, quasicrystals fall somewhere between a crystal, like a diamond, which has a regular repeating structure, and an amorphous material, like glass, “where the atoms are all mixed together or randomly arranged,” de la Barrera explains. In a nutshell, quasicrystals “have really strange patterns,” says de la Barrera (see some examples here).
However, compared to crystals and amorphous materials, relatively little is known about quasicrystals. This is partly because they are difficult to make. “That’s not to say they’re not interesting; it just means that we haven’t paid as much attention to them, especially to their electronic properties,” says de la Barrera. The new, relatively simple platform could be a game-changer.
Because the original researchers were not experts in quasicrystals, they contacted someone who was: Professor Ron Lifshitz of Tel Aviv University. Aviram Uri, one of the paper’s co-first authors and a postdoctoral fellow at MIT Pappalardo and VATAT, was a student of Lifshitz during his undergraduate studies in Tel Aviv and was familiar with his work on quasicrystals. Lifshitz, who is also the author of Nature paper, helped the team better understand what they were looking at, what they call a moiré quasicrystal.
Physicists then tuned a moiré quasicrystal to make it superconductive, or transmit current without any resistance below a certain low temperature. This is important because superconducting devices could transfer current through electronic devices much more efficiently than today, but the phenomenon is not yet fully understood in all cases. The new system of moire quasicrystals provides a new way to study it.
The team also found evidence of symmetry breaking, another phenomenon that “tells us that electrons are interacting very strongly with each other.” And as physicists and quantum materials scientists, we want our electrons to interact with each other, because that’s where the exotic physics happens,” de la Barrera explains.
Ultimately, “through discussions across continents, we were able to decipher this thing, and now we think we have a good idea of what’s going on,” says Uri, while noting that “we don’t understand yet the system completely. There are still quite a few mysteries remaining. »
The best part of the research was “solving the puzzle of what we had actually created,” says de la Barrera. “We were expecting (something else), so it was a very pleasant surprise when we realized we were actually looking at something very new and different.”
“It’s the same answer for me,” Uri said.
Additional authors of Nature the article is Raymond C. Ashoori, professor of physics at MIT; Mallika T. Randeria, a researcher at MIT Lincoln Laboratory who led the work as a Pappalardo Fellow at MIT and is another co-first author of the paper; Trithep Devakul, an assistant professor at Stanford University who conducted the work as a postdoctoral fellow at MIT; Philip JD Crowley, postdoctoral fellow at Harvard University; and Kenji Watanabe and Takashi Taniguchi of the National Institute of Materials Science in Japan.
This work was supported by the US Army Research Office, the US National Science Foundation, the Gordon and Betty Moore Foundation, an MIT Pappalardo Fellowship, a TVAT Outstanding Postdoctoral Fellowship in Quantum Science and Technology, JSPS KAKENHI and the Israel Science Foundation.