A group of MIT physicists recently discovered that carbon stacked in a particular way behaves like an unconventional superconductor.
Superconductors are critical to current and future technological innovations. They function by providing effectively no electrical resistance when cooled below a certain temperature, called the critical temperature. Technologies such as MRI machines, maglev trains, quantum computers, particle accelerators, and future nuclear fusion reactors all critically rely on this property.
Typically, conventional superconductors require ultra-low critical temperatures to operate, which can involve complex, expensive cooling systems. If superconductors could work closer to room temperature, entirely new technological possibilities could emerge, such as lossless power grids, more precise medical imaging, and more capable quantum computers.
A recent discovery out of MIT is generating excitement in the world of superconductors. In November, researchers reported new and direct evidence that a carbon-based material known as “magic-angle” twisted tri-layer graphene (MATTG) behaves as an unconventional superconductor. The material is created by stacking three atomically thin sheets of graphene at a very specific angle, allowing unusual electrical properties to appear.
Scientists have suspected for years that twisted graphene structures might host unconventional superconductivity, but proof has remained elusive. The new work, published in Science, offers the clearest confirmation yet.
What makes unconventional superconductors so interesting is that they do not follow the traditional governing rules of superconductors. In conventional superconductors, electrons pair up through vibrations in the atomic lattice. These pairs, called Cooper pairs, allow electricity to flow without resistance. But in unconventional superconductors, the electrons appear to pair through a completely different mechanism that scientists still do not fully understand. Because of this, many of these materials operate at higher temperatures than their conventional counterparts.
Using a new experimental platform, the MIT team was able to directly measure MATTG’s superconducting gap, an energy signature that reflects how strongly electrons are paired. What they found was striking: instead of the smooth, uniform gap observed in conventional superconductors, MATTG displayed a distinct V-shaped gap profile. This shape strongly suggests that the material has “nodes,” or directions in which electrons don’t participate in pairing, one of the defining characteristics of unconventional superconductors.
Confirming this behavior is a major milestone because graphene-based superconductors are structurally simple, just carbon, making them easier to model and study than many complex unconventional superconductors previously discovered. By probing how electrons pair in this cleaner system, researchers hope to finally crack the mechanism of unconventional superconductivity.
While room-temperature superconductors are still a long way off, discoveries like this bring researchers one step closer to technologies that today sound like science fiction, but may not stay that way for long.
