Researchers from MIT and Japan's National Institute for Materials Science have made a groundbreaking discovery in the field of superconductivity. They have observed key evidence of unconventional superconductivity in a unique material called magic-angle twisted tri-layer graphene (MATTG). This material is created by stacking three atomically-thin sheets of graphene at a specific angle, which gives it extraordinary properties. MATTG has previously shown indirect signs of unconventional superconductivity, but this new study provides the most direct confirmation yet. The team was able to measure the superconducting gap of MATTG, a property that indicates the resilience of its superconducting state at different temperatures. Interestingly, the superconducting gap of MATTG differs significantly from that of conventional superconductors, suggesting a unique mechanism for its superconductivity. This discovery could potentially lead to the development of room-temperature superconductors, which would be a significant advancement for human society. The researchers achieved this by using a new experimental platform that allows them to observe the superconducting gap in real-time as the superconductivity emerges in two-dimensional materials. This platform will be further utilized to study MATTG and other 2D materials, potentially uncovering promising candidates for future technologies. The study's co-lead author, Shuwen Sun, emphasizes the importance of understanding unconventional superconductors, as they may hold the key to developing superconductors that operate at room temperature. This understanding could guide the design of advanced superconductors, a goal that has been pursued in the field for decades. The discovery of magic-angle graphene in 2018 by Pablo Jarillo-Herrero and his colleagues sparked a new field called 'twistronics,' focusing on atomically thin, precisely twisted materials. Since then, their research has explored various configurations of magic-angle graphene and other two-dimensional materials, uncovering signs of unconventional superconductivity. Superconductivity is a phenomenon where materials can conduct electricity without resistance at extremely low temperatures. In superconductors, electrons form pairs called Cooper pairs, allowing them to move through the material without friction. The way these electron pairs are formed can vary, leading to different types of superconductivity. Jeong Min Park, another co-lead author, highlights the unique nature of magic-angle graphene's electron pairs, which are tightly bound, almost like a molecule. This tight binding is a distinctive feature of this material. The researchers' new study aimed to directly observe and confirm unconventional superconductivity in magic-angle graphene by measuring its superconducting gap. They developed an experimental platform combining electron tunneling with electrical transport, a technique used to measure superconductivity. By combining these measurements, they could identify the superconducting tunneling gap, which appeared only when the material exhibited zero electrical resistance, a characteristic of superconductivity. The gap displayed a V-shaped profile, distinct from the flat shape of conventional superconductors, providing evidence of an unconventional superconducting mechanism. The exact mechanism remains unknown, but it suggests that electrons in MATTG pair up through a different process, possibly involving strong electronic interactions rather than lattice vibrations. This discovery opens up new avenues for research, as the team plans to explore other two-dimensional twisted structures and materials using the new experimental platform. This approach will enable a deeper understanding of superconductivity and other quantum phases, potentially leading to the development of advanced superconductors and quantum materials.
