For decades, physicists have been trying to answer a fundamental question: Can electrons move like a perfectly smooth, frictionless fluid governed by universal quantum values? Detecting this anomalous behavior has proven to be extremely difficult. In real materials, small defects such as atomic defects or impurities tend to interfere with these delicate quantum effects, making them nearly impossible to observe.
Now, researchers from the Department of Physics, Indian Institute of Science (IISc), in collaboration with collaborators from Japan’s National Institute for Materials Science, have finally identified this elusive quantum fluid in graphene. This material consists of a single layer of carbon atoms arranged in flat sheets. Their discovery is natural physicsopens new avenues for studying quantum phenomena and positions graphene as a powerful platform for exploring effects that have hitherto been out of reach in laboratory settings.
“It’s amazing that a single layer of graphene can do so much even 20 years after its discovery,” said Arindam Ghosh, professor in IISc’s Department of Physics and one of the study’s corresponding authors.
breaking the basic laws of physics
To uncover this behavior, the team created extremely clean graphene samples and carefully measured how they conduct both electricity and heat. What they discovered was unexpected. The two traits moved in opposite directions instead of increasing together. As electrical conductivity increases, thermal conductivity decreases and vice versa.
This result directly contradicts the Wiedemann-Franz law, a well-established principle that heat and electrical conduction in metals should be proportional. The researchers observed that the deviation from this law was more than 200 times greater at low temperatures, revealing a significant gap between charge and heat moving through the material.
universal quantum connection
Despite this unusual division, its behavior is not random. Both types of conduction appear to obey universal constants that do not depend on the material itself. This constant is related to the quantum of conductance, a fundamental quantity that describes how electrons move on the smallest scales.
Dirac fluid and liquid electrons
This remarkable effect occurs in a special condition known as the “Dirac point,” where graphene is located at the boundary between metal and insulator. By adjusting the number of electrons, researchers can arrive at this precise state.
At this point, the electrons stop behaving like individual particles. Instead, they move collectively, flowing like a liquid. This fluid-like movement is similar to water, but with much less resistance to flow. “This water-like behavior is observed near the Dirac point, so it is called a Dirac fluid. It is an exotic state of matter that mimics the quark-gluon plasma, a soup of high-energy subatomic particles observed in CERN’s particle accelerator,” says first author Aniket Majumdar, a doctoral student in the Department of Physics. The researchers also measured how easily the fluid flowed and found that its viscosity was extremely low, making it the closest to a perfect fluid ever observed.
A new window into extreme physics
These results establish graphene as an accessible and cost-effective system for exploring ideas typically associated with extreme environments. Scientists can now investigate phenomena related to high-energy physics and astrophysics, such as the thermodynamics of black holes and the scaling of entanglement entropy, in a laboratory setting.
Future applications of quantum technology
Beyond its scientific importance, this discovery could have practical implications. The presence of Dirac fluids in graphene could enable the development of highly sensitive quantum sensors. Such devices can amplify very weak electrical signals and detect weak magnetic fields, opening the door to new techniques in sensing and measurement.
