MIT quantum breakthrough edges toward room-temp superconductors

However, these "conventional" superconductors only operate at extremely cold temperatures. They must be kept in specialized cooling systems to remain in their superconducting state. If materials could superconduct at warmer, more practical temperatures, they could transform modern technology -- from creating energy grids that waste no power to enabling more functional quantum computers. To reach that goal, researchers at MIT and other institutions are exploring "unconventional" superconductors, materials that defy the rules of traditional ones and may lead to the next big breakthrough.

MIT's Magic-Angle Graphene Discovery

In a major step forward, MIT physicists have observed clear evidence of unconventional superconductivity in "magic-angle" twisted tri-layer graphene (MATTG). This unique material is created by stacking three atom-thin sheets of graphene at a very specific angle. That tiny twist dramatically alters the material's properties, giving rise to strange and promising quantum effects.

While earlier studies hinted that MATTG might host unconventional superconductivity, the new findings, published in Science, offer the most direct confirmation to date.

A New Look at the Superconducting Gap

The MIT team successfully measured MATTG's superconducting gap, which indicates how strong a material's superconducting state is at different temperatures. They found that the gap in MATTG looked completely different from what is seen in conventional superconductors. This difference suggests that the way MATTG becomes superconducting relies on a distinct, unconventional mechanism.

"There are many different mechanisms that can lead to superconductivity in materials," explains co-lead author Shuwen Sun, a graduate student in MIT's Department of Physics. "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."

The team made this discovery with a new experimental system that lets them directly observe how the superconducting gap forms in two-dimensional materials. They plan to use the technique to study MATTG and other 2D materials in more detail, hoping to identify new candidates for advanced technologies.

"Understanding one unconventional superconductor very well may trigger our understanding of the rest," says Pablo Jarillo-Herrero, the Cecil and Ida Green Professor of Physics at MIT and senior author of the study. "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 Origins of Twistronics

Graphene is made of a single layer of carbon atoms arranged in a hexagonal pattern that looks like chicken wire. Scientists can peel off a sheet of graphene from graphite (the same material in pencil lead) to study its properties. In the 2010s, researchers predicted that stacking two layers of graphene at a very precise angle could create new electronic behaviors.

In 2018, Jarillo-Herrero's group became the first to experimentally produce this so-called "magic-angle" graphene and reveal its extraordinary properties. That work launched a new field of research known as "twistronics," which studies the surprising effects that emerge when ultra-thin materials are stacked and twisted at exact orientations. Since then, the team and others have explored a variety of graphene structures with multiple layers, revealing further signs of unconventional superconductivity.

How Electrons Cooperate

Superconductivity occurs when electrons form pairs rather than scattering apart as they move through a material. These paired electrons, known as "Cooper pairs," can travel without resistance, creating a perfect flow of current.

"In conventional superconductors, the electrons in these pairs are very far away from each other, and weakly bound," says 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. There were hints that there is something very different about this material."

Probing the Quantum World Through Tunneling

To prove that MATTG truly exhibits unconventional superconductivity, the MIT researchers needed to measure its superconducting gap directly. As Park explains, "When a material becomes superconducting, electrons move together as pairs rather than individually, and there's an energy 'gap' that reflects how they're bound. The shape and symmetry of that gap tells us the underlying nature of the superconductivity."

To do this, scientists used a quantum-scale technique known as tunneling spectroscopy. At this level, electrons act both as particles and as waves, which allows them to "tunnel" through barriers that would normally stop them. By studying how easily electrons can tunnel through a material, researchers can learn how strongly they are bound inside it. However, tunneling results alone don't always prove that a material is superconducting, making direct measurements both crucial and challenging.

A Closer Look at the Superconducting Gap

Park's team developed a new platform that combines tunneling spectroscopy with electrical transport measurements, which involve tracking how current moves through the material while monitoring its resistance (zero resistance means it's superconducting).

Using this method on MATTG, the researchers could clearly pinpoint the superconducting tunneling gap -- it appeared only when the material reached zero resistance, the defining mark of superconductivity. As they changed the temperature and magnetic field, the gap displayed a sharp V-shaped curve, very different from the smooth, flat pattern typical of conventional superconductors.

This unusual V shape points to a new mechanism behind MATTG's superconductivity. Although the exact process is still unknown, it's now clear that this material behaves unlike any conventional superconductor discovered before.

A Different Kind of Electron Pairing

In most superconductors, electrons pair up due to vibrations in the surrounding atomic lattice, which gently push them together. Park believes MATTG operates differently.

"In this magic-angle graphene system, there are theories explaining that the pairing likely arises from strong electronic interactions rather than lattice vibrations," she says. "That means electrons themselves help each other pair up, forming a superconducting state with special symmetry."

The Path Ahead: Next-Generation Quantum Materials

The MIT team plans to apply their new experimental setup to study other twisted and layered materials.

"This allows us to both identify and study the underlying electronic structures of superconductivity and other quantum phases as they happen, within the same sample," Park explains. "This direct view can reveal how electrons pair and compete with other states, paving the way to design and control new superconductors and quantum materials that could one day power more efficient technologies or quantum computers."

This research received support from the U.S. Army Research Office, the U.S. Air Force Office of Scientific Research, the MIT/MTL Samsung Semiconductor Research Fund, the Sagol WIS-MIT Bridge Program, the National Science Foundation, the Gordon and Betty Moore Foundation, and the Ramon Areces Foundation.