MIT scientists and their collaborators have unveiled a groundbreaking study that may rekindle interest in the mysterious realm of quasicrystals. Their research, recently published in Nature, introduces an innovative method to craft atomically thin versions of quasicrystals, offering the ability to customize these materials to exhibit intriguing properties, including superconductivity.
This research not only provides a novel approach to delving deeper into the realm of quasicrystals but also opens up avenues for investigating elusive phenomena that are typically challenging to explore. These endeavors hold the potential to lead to significant applications and new insights into physics. For instance, gaining a more profound understanding of superconductivity, where electrons flow through a material without resistance, could revolutionize the efficiency of electronic devices.
What makes this study truly exceptional is its fusion of two previously unrelated fields: quasicrystals and twistronics. Twistronics, a discipline pioneered at MIT only half a decade ago by Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT and the paper’s corresponding author, continues to forge unexpected connections with other domains of physics and chemistry. In this case, it unites with the captivating world of quasiperiodic crystals, marking yet another remarkable stride in scientific exploration.
Do the twist
Twistronics revolves around stacking atomically thin layers of materials on top of each other and introducing a subtle twist, or rotation, to create a fascinating pattern known as a moiré superlattice. This moiré pattern has a profound influence on the behavior of electrons.
By altering the angle of rotation or the number of electrons within the system, researchers can tailor moiré systems to exhibit different behaviors, sparking a surge of interest in twistronics over the past half-decade. Scientists worldwide have harnessed this approach to craft new atomically thin quantum materials, yielding remarkable outcomes. Here are some examples from MIT:
Transformation of magic-angle twisted bilayer graphene into three distinct and practical electronic devices, showcased in a 2021 study. The team behind this work, including co-first author Daniel Rodan-Legrain, who was a postdoctoral associate at MIT, was led by Jarillo-Herrero.
Introduction of ferroelectricity, a unique property, into a well-established group of semiconductors, highlighted in a 2021 research endeavor led by Jarillo-Herrero.
The prediction of exotic magnetic phenomena, complete with a “recipe” for their realization, as detailed in a 2023 study. This project featured contributions from MIT Professor of Physics Liang Fu and Nisarga Paul, an MIT graduate student in physics, both of whom are co-authors of the recent paper.
Toward new quasicrystals
In their latest study, the researchers were experimenting with a moiré system composed of three layers of graphene. Graphene, as you may know, consists of a single layer of carbon atoms arranged in hexagonal patterns resembling a honeycomb structure. In this particular experiment, the team stacked three graphene sheets on top of each other but introduced a twist to two of the layers at slightly different angles.
To their astonishment, this setup generated a quasicrystal—a rather peculiar class of material that was first unearthed in the 1980s. As the name suggests, quasicrystals fall somewhere in between traditional crystals, like diamonds, which exhibit regular repeating structures, and amorphous materials, such as glass, where atoms are haphazardly arranged. In essence, quasicrystals are known for their truly unconventional and intricate patterns.
However, when compared to crystals and amorphous substances, quasicrystals remain relatively enigmatic. One reason is that they are challenging to fabricate. This doesn’t diminish their significance; it simply means they haven’t received as much attention, particularly in terms of their electronic properties. The introduction of this new, relatively straightforward platform has the potential to change that by opening up opportunities for exploring quasicrystals more deeply.
The original researchers, not having expertise in quasicrystals, sought guidance from an authority in the field, Professor Ron Lifshitz from Tel Aviv University. Aviram Uri, one of the co-first authors of the paper and an MIT Pappalardo and VATAT Postdoctoral Fellow, had been a student of Lifshitz during his undergraduate years at Tel Aviv University and was aware of Lifshitz’s quasicrystal research. Lifshitz, also a co-author of the Nature paper, played a pivotal role in helping the team comprehend their discovery, which they refer to as a moiré quasicrystal.
The physicists then fine-tuned this moiré quasicrystal to induce superconductivity, a state in which current flows with zero resistance at very low temperatures. This development holds significant promise as superconducting devices could drastically enhance the efficiency of electronic devices. However, the complete understanding of superconductivity remains an ongoing challenge, and the new moiré quasicrystal system offers a fresh avenue for its investigation.
Furthermore, the team uncovered evidence of symmetry breaking, a phenomenon indicating robust electron interactions. These strong electron interactions are of particular interest to physicists and quantum material scientists, as they often lead to the emergence of exotic physical phenomena.
In the end, through collaborative efforts spanning continents, the researchers unraveled the puzzle of their creation, yet they acknowledge that some mysteries remain unsolved. Aviram Uri highlights that while they have gained valuable insights, a complete understanding of the system is still a work in progress.
The most rewarding aspect of this research, according to Sergio C. de la Barrera, was the unexpected revelation of something entirely new and different from their initial expectations. Aviram Uri shares the sentiment, emphasizing the excitement of this discovery.