Electrons in Ultra-Pure Graphene Form a Frictionless Quantum Liquid — Defying a 150-Year-Old Law of Physics by 200-Fold

Scientists at the Indian Institute of Science (IISc) in Bangalore have observed electrons in ultra-pure graphene flowing like a nearly frictionless quantum liquid — violating one of the most fundamental laws of condensed matter physics by a factor of more than 200, according to research published Wednesday in the journal Nature Physics.

The discovery hinges on a condition called the "Dirac point," the precise energy at which graphene transitions between behaving as a metal and behaving as an insulator. At this quantum boundary, in samples of graphene so clean that defects are vanishingly rare, the researchers found that electrons stop acting as individual particles and instead collectively form what physicists call a "Dirac fluid" — an exotic state of matter that had not previously been directly observed in an ordinary solid at low temperatures.

The finding directly violates the Wiedemann-Franz law, a pillar of classical physics established more than 150 years ago, which holds that electrical and thermal conductivity in metals must always remain proportional to each other. In ordinary metals, when electrons carry electricity, they inevitably carry heat as well, and the ratio between the two conduction pathways is governed by a universal constant. In the Dirac fluid state discovered by the IISc team, the relationship between electrical and thermal conductivity diverged by more than 200-fold at low temperatures — a deviation so extreme it was initially difficult for the team to believe they were measuring the same material. "It is amazing that there is so much to do on just a single layer of graphene even after 20 years of discovery," said Professor Arindam Ghosh, the study's corresponding author.

The Dirac fluid state is theoretically analogous to the quark-gluon plasma created in particle accelerators at CERN — the fleeting state of matter that existed in the first microseconds after the Big Bang, when quarks had not yet assembled into protons and neutrons. "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," said Aniket Majumdar, the study's first author and a PhD student in Ghosh's group at IISc's Department of Physics. The comparison underscores the peculiarity of finding Big Bang-like collective behavior in a material that can be produced on a laboratory bench from a single atomic layer of carbon.

The research was conducted in collaboration with scientists at the National Institute for Materials Science in Japan. Achieving the result required pushing graphene sample quality far beyond what is routinely available, since any impurity or defect in the lattice disrupts the collective behavior and returns electrons to their conventional individual-particle dynamics. The team used a combination of careful fabrication techniques and cryogenic measurements at temperatures just a few degrees above absolute zero to access the Dirac point conditions under which the fluid state emerges.

The implications of the discovery extend well beyond fundamental physics. A material in which heat and electricity decouple so dramatically could enable a new generation of quantum sensors capable of detecting extraordinarily faint magnetic fields and amplifying extremely weak electrical signals. Potential applications range from brain imaging using magnetoencephalography to searches for dark matter and to geological surveys conducted in remote or extreme environments. The discovery also opens a new experimental window into hydrodynamic quantum transport — the study of how quantum particles flow collectively like fluids — a field that has so far been largely confined to theoretical predictions.

Graphene, a single atom-thick sheet of carbon atoms arranged in a hexagonal lattice, was first isolated in 2004 by Andre Geim and Konstantin Novoselov at the University of Manchester, who shared the 2010 Nobel Prize in Physics for the achievement. In the more than two decades since, it has been the subject of thousands of scientific papers and has proven a near-inexhaustible source of surprising quantum phenomena. The Dirac fluid discovery adds a new chapter to that history, suggesting that even well-understood materials can yield fundamental surprises when pushed to sufficient purity and probed at the right energy scales.