Physicists at MIT have observed direct evidence of unconventional superconductivity in magic-angle twisted tri-layer graphene, revealing a distinctive V-shaped energy gap. This breakthrough suggests electron pairing driven by strong interactions rather than lattice vibrations. The findings, published in Science, could pave the way for room-temperature superconductors.
Superconductors enable electricity to flow without resistance, powering technologies like MRI scanners and particle accelerators. However, conventional ones require extremely low temperatures, limiting their use. Researchers seek unconventional materials that might operate at warmer conditions, potentially revolutionizing energy grids and quantum computers.
In a key advance, MIT physicists studied magic-angle twisted tri-layer graphene (MATTG), created by stacking three atom-thin graphene sheets at a precise angle. This configuration alters the material's properties, fostering quantum effects. Earlier work hinted at unconventional superconductivity in MATTG, but the new study provides the clearest confirmation yet.
The team measured the superconducting gap, which shows the strength of the superconducting state. Unlike the smooth, flat gap in conventional superconductors, MATTG's gap forms a sharp V-shape, indicating a different mechanism. "The superconducting gap gives us a clue to what kind of mechanism can lead to things like room-temperature superconductors that will eventually benefit human society," says co-lead author Shuwen Sun, a graduate student in MIT's Department of Physics.
Using a novel setup combining tunneling spectroscopy and electrical transport measurements, the researchers confirmed the gap appears only at zero resistance, the hallmark of superconductivity. As temperatures and magnetic fields changed, the V-shape persisted, pointing to electron pairs tightly bound like molecules.
"In conventional superconductors, the electrons in these pairs are very far away from each other, and weakly bound," explains co-lead author Jeong Min Park, PhD '24. "But in magic-angle graphene, we could already see signatures that these pairs are very tightly bound, almost like a molecule."
This pairing likely stems from strong electronic interactions, not atomic vibrations. The discovery builds on 2018 experiments by senior author Pablo Jarillo-Herrero's group, which launched twistronics—a field exploring twisted ultra-thin materials.
"Understanding one unconventional superconductor very well may trigger our understanding of the rest," says Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT. "This understanding may guide the design of superconductors that work at room temperature, for example, which is sort of the Holy Grail of the entire field."
The team plans to apply their technique to other 2D materials, aiming to uncover new quantum phases and advance technologies like efficient power systems and quantum computing. The research appears in Science (DOI: 10.1126/science.adv8376).