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 material known as magic-angle twisted tri-layer graphene (MATTG). This material is created by stacking three atomically-thin sheets of graphene at a specific angle, or twist, which allows for the emergence of exotic properties. MATTG has previously shown indirect hints of unconventional superconductivity and strange electronic behavior. The new study provides the most direct confirmation yet of this phenomenon. Specifically, the team was able to measure MATTG's superconducting gap, a property that describes the resilience of a material's superconducting state at given temperatures. They found that MATTG's superconducting gap differs significantly from that of typical superconductors, indicating a unique mechanism for its superconductivity. This discovery could lead to the development of room-temperature superconductors, which would have a profound impact on human society. The researchers achieved this breakthrough by using a new experimental platform that allows them to 'watch' the superconducting gap in real-time as superconductivity emerges in two-dimensional materials. This platform will be used to further investigate MATTG and map the superconducting gap in other 2D materials, potentially revealing promising candidates for future technologies. Understanding unconventional superconductors may unlock the design of superconductors that work at room temperature, a goal that could revolutionize the field. In 2018, MIT's Pablo Jarillo-Herrero and his colleagues were the first to produce magic-angle graphene and observe its extraordinary properties. This discovery sparked a new field called 'twistronics', focusing on atomically thin, precisely twisted materials. Jarillo-Herrero's group has since explored various configurations of magic-angle graphene and other 2D materials, uncovering signatures of unconventional superconductivity. Superconductivity is a state where materials can exhibit certain properties at very low temperatures, allowing electrons to pair up and move without friction. The way electrons are bound in these pairs can vary, leading to different types of superconductors. In conventional superconductors, electrons are weakly bound, but in MATTG, the pairs are tightly bound, almost like a molecule. This unique binding suggests a different mechanism for superconductivity in MATTG. The study's co-lead authors, Shuwen Sun and Jeong Min Park, developed an experimental platform combining electron tunneling and electrical transport to measure the superconducting gap in MATTG. This platform allowed them to directly observe the unconventional superconductivity and track the evolution of the gap under varying conditions. The V-shaped profile of the gap is a key indicator of the unconventional mechanism at play. While the exact mechanism remains unknown, the distinct shape of the superconducting gap in MATTG provides strong evidence of its unconventional nature. This discovery opens up new possibilities for understanding and designing unconventional superconductors, potentially leading to more efficient technologies and quantum computers.
