Physicists Detect Elusive Quantum Fluid in Graphene, Breaking Fundamental Law of Physics

A Decades-Long Quest Comes to Fruition

For more than twenty years, physicists have pursued an enigmatic target: observing electrons behaving as a perfectly smooth, frictionless quantum fluid. The challenge has always been formidable. Real materials are riddled with atomic defects and impurities that sabotage the delicate quantum effects required for this phenomenon to emerge. Now, researchers at the Indian Institute of Science (IISc) in India, collaborating with the National Institute for Materials Science in Japan, have finally captured this ghostly behavior—in graphene, a material consisting of a single layer of carbon atoms arranged in a flat sheet.

Their breakthrough, published in *Nature Physics*, represents a watershed moment for quantum materials science. "It is amazing that there is so much to do on just a single layer of graphene even after 20 years of discovery," says Arindam Ghosh, Professor at the Department of Physics at IISc and a corresponding author. The discovery opens new experimental avenues for studying quantum phenomena that were previously accessible only in theory or extreme environments.

Violating a 150-Year-Old Law

The team's approach was deceptively elegant: they fabricated exceptionally clean graphene samples and meticulously measured how the material conducts both electricity and heat. What emerged was astonishing. Rather than moving in tandem as classical physics would predict, electrical conductivity and thermal conductivity moved in opposite directions. As one rose, the other fell.

This result directly contradicts the Wiedemann-Franz law, a cornerstone principle established in the 19th century stating that electrical and thermal conduction in metals must be proportional to each other. The researchers observed deviations exceeding 200 times at low temperatures—a staggering violation of one of physics' most fundamental rules.

"Instead of increasing together, the two properties moved in opposite directions. As electrical conductivity rose, thermal conductivity dropped, and vice versa."

Yet the violation is not chaotic. Both types of conduction follow a universal constant independent of the material itself, rooted in the quantum of conductance—a fundamental quantity describing electron behavior at the smallest scales. This universality suggests something profound is happening at a deeper level of reality.

The Dirac Fluid: Electrons as a Liquid

The phenomenon occurs at a special quantum threshold called the "Dirac point," where graphene sits on a knife's edge between metallic and insulating states. By adjusting the number of electrons in the material, researchers can fine-tune the system to this precise condition. At this boundary, electrons abandon their individual particle nature and instead move collectively, flowing like a liquid with extraordinarily low resistance.

"Since this water-like behaviour is found near the Dirac point, it is called a Dirac fluid—an exotic state of matter which mimics the quark-gluon plasma, a soup of highly energetic subatomic particles observed in particle accelerators at CERN," explains Aniket Majumdar, the study's first author and a PhD student at IISc. Remarkably, measurements of the fluid's viscosity reveal it to be extremely low, making it one of the closest experimental realizations of a perfect, frictionless fluid ever observed in a laboratory.

This liquid-like behavior of electrons has profound theoretical implications. It suggests that the quantum world operates according to principles of hydrodynamics—the same mathematics that governs water flowing through pipes—but at scales where quantum mechanics dominates. The discovery validates decades of theoretical speculation and bridges gaps between high-energy physics and condensed matter science.

A Laboratory Window Into Extreme Cosmic Physics

The implications extend far beyond graphene itself. This work establishes a new experimental platform for investigating phenomena ordinarily associated with extreme environments: the interiors of black holes, the earliest moments after the Big Bang, or the conditions inside particle accelerators at CERN. Scientists can now study black-hole thermodynamics, entanglement entropy scaling, and other exotic physics in a tabletop setting using readily available materials.

"Scientists can now investigate phenomena linked to high-energy physics and astrophysics within a laboratory setting."

This democratization of extreme-physics research could accelerate discovery across multiple disciplines. Theoretical predictions can be tested in real time without requiring multi-billion-dollar particle accelerators or observations of distant astronomical phenomena.

Practical Quantum Technology on the Horizon

Beyond fundamental science, the discovery carries practical promise. The presence of a Dirac fluid in graphene may enable development of highly sensitive quantum sensors capable of detecting extraordinarily weak electrical signals and faint magnetic fields. Such devices could revolutionize measurement technology and unlock new applications in quantum sensing, potentially transforming fields from medical diagnostics to fundamental physics experiments.