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MIT Discovers Magnetic Superconductor in Pencil Lead

Scientists at MIT have discovered something that shouldn’t exist: a material that conducts electricity without resistance while simultaneously acting as a magnet.

This “chiral superconductor” was found hiding in ordinary graphite—the same carbon-based material used in pencil lead. The discovery, published today in Nature, challenges a century-old assumption that magnetism and superconductivity are incompatible, like oil and water.

The finding emerged from experiments with rhombohedral graphene, a special arrangement of carbon atoms stacked like a staircase. When cooled to just 300 millikelvins—nearly absolute zero—this material exhibits zero electrical resistance while maintaining magnetic properties.

Breaking the Rules of Physics

“The general lore is that superconductors do not like magnetic fields,” says Long Ju, assistant professor of physics at MIT and senior author of the study. “But we believe this is the first observation of a superconductor that behaves as a magnet with such direct and simple evidence.”

The discovery overturns decades of established physics. Since 1911, scientists have known that superconductors repel magnetic fields through the Meissner effect. This magnetic repulsion is what enables magnetic levitation trains, where superconducting rails push away magnetized cars.

But MIT’s material does something different entirely. When researchers applied external magnetic fields and swept them from negative to positive—like flipping between north and south poles—the material switched between two distinct superconducting states while maintaining zero resistance.

The Graphite Connection

The team wasn’t initially hunting for magnetic superconductors. They were studying pentalayer rhombohedral graphene—five sheets of carbon atoms arranged in an offset, staircase pattern. This structure occasionally forms tiny pockets within ordinary graphite.

Most graphite contains millions of graphene sheets stacked in regular alignment. But these rare rhombohedral regions, resembling misaligned building blocks, create entirely different electronic properties.

“If this were a conventional superconductor, it would just remain at zero resistance, until the magnetic field reaches a critical point, where superconductivity would be killed,” explains Zach Hadjri, a first-year student in the group. “Instead, this material seems to switch between two superconducting states, like a magnet that starts out pointing upward, and can flip downwards when you apply a magnetic field.”

Quantum Mechanics at Work

The secret lies in how electrons behave at ultracold temperatures. In conventional superconductors, electrons pair up as “Cooper pairs” and glide through materials without resistance. These pairs typically have zero overall momentum and don’t spin.

But in rhombohedral graphene, something unusual happens. All electrons collectively occupy the same “valley”—a quantum mechanical momentum state. When these electrons pair up, their combined momentum doesn’t cancel out.

“You can think of the two electrons in a pair spinning clockwise, or counterclockwise, which corresponds to a magnet pointing up, or down,” explains Tonghang Han, a fifth-year student in the group. “So we think this is the first observation of a superconductor that behaves as a magnet due to the electrons’ orbital motion, which is known as a chiral superconductor.”

Key Findings from the Research:

  • Material maintains superconductivity up to 300 millikelvin temperature
  • Shows magnetic hysteresis—switching between magnetic states—while superconducting
  • Critical magnetic field reaches 1.4 Tesla, higher than other graphene superconductors
  • Exhibits strong-coupling superconductivity near the BCS-BEC crossover
  • Demonstrates charge density as low as 2.4×10¹¹ cm⁻²

Beyond the Headlines

What makes this discovery particularly intriguing is a detail that extends beyond typical coverage: the material operates in what physicists call the “BCS-BEC crossover” regime. This represents a frontier area where superconductivity transforms from loosely bound Cooper pairs (BCS theory) to tightly bound pairs that behave more like a quantum fluid (BEC, or Bose-Einstein condensate).

The high critical magnetic field of 1.4 Tesla suggests these electron pairs are unusually robust, indicating strong-coupling superconductivity that bridges fundamental quantum mechanical regimes. This crossover behavior could unlock new physics principles that don’t apply to conventional superconductors.

Implications for Quantum Computing

The discovery has profound implications for quantum technology. Chiral superconductors are candidates for hosting Majorana fermions—exotic particles that could revolutionize quantum computing by making it more fault-tolerant.

“It’s one of a kind,” Han notes. “It is also a candidate for a topological superconductor which could enable robust quantum computation.”

Current quantum computers are fragile, losing information when disturbed by environmental noise. Majorana fermions, if they exist in this material, could store quantum information in a way that’s naturally protected from such disturbances.

“It is truly remarkable that such an exotic chiral superconductor emerges from such simple ingredients,” adds Liang Fu, professor of physics at MIT. The team observed identical behavior across six different samples, confirming the phenomenon’s reproducibility.

Could the next quantum computing breakthrough come from something as mundane as pencil lead? The MIT team’s discovery suggests that extraordinary physics might be hiding in the most ordinary materials, waiting for the right conditions to reveal themselves.

 

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