Graphene Electrons Defy 150-Year-Old Physics Law by a Factor of 200, Nature Physics Reports

Scientists at the Indian Institute of Science in Bangalore have shattered a cornerstone of classical physics that has stood for more than 150 years, publishing results showing that electrons in a single layer of carbon atoms can conduct electricity and heat in opposite directions — a phenomenon that violates the Wiedemann-Franz Law and opens a window onto exotic states of matter previously seen only in particle accelerators.

The discovery, published in Nature Physics and announced publicly on April 15, was made by a team led by Professor Arindam Ghosh and PhD student Aniket Majumdar, working in collaboration with researchers at Japan's National Institute for Materials Science. In single-layer graphene — a sheet of carbon atoms arranged in a hexagonal lattice exactly one atom thick — the team measured electrical and thermal conductivity simultaneously under precisely controlled conditions and found the two quantities moving in opposite directions near a quantum threshold known as the Dirac point.

The Wiedemann-Franz Law, established in 1853 by German physicists Gustav Wiedemann and Rudolf Franz, states that in any metal, the ratio of electrical conductivity to thermal conductivity at a given temperature is a near-universal constant known as the Lorenz number. The law holds with remarkable consistency across virtually every metal ever tested — copper, aluminum, iron, silver, gold — and underpins most modern electronic engineering. The IISc team's graphene samples violated the law by more than 200 times at low temperatures, the most dramatic deviation ever recorded in any material.

The violation occurs because graphene near the Dirac point hosts a collective state of electrons called a "Dirac fluid" — in which electrons behave not as independent particles but as an extremely low-viscosity liquid that flows collectively. This hydrodynamic electron state conducts electricity efficiently while allowing heat to disperse through a separate mechanism, decoupling the two quantities in a way that classical metal physics forbids. The electron fluid in graphene is one of the closest experimental realizations of a perfect fluid ever observed in any material, mimicking the quark-gluon plasma studied at the Large Hadron Collider — but achievable at temperatures accessible in a university laboratory rather than requiring a particle accelerator.

The breakthrough was made possible only by manufacturing graphene samples of exceptional purity. In ordinary graphene, atomic-scale impurities scatter electrons before they can establish collective fluid behavior, masking the effect entirely. The IISc team spent years perfecting fabrication techniques that eliminate contaminants, clearing the way to observe physics that has existed in graphene since its discovery in 2004 but remained hidden beneath experimental noise.

Potential applications include ultra-sensitive quantum sensors capable of detecting faint magnetic fields, novel amplifiers for weak electrical signals, and new fundamental tools for studying collective quantum phenomena. Ghosh reflected on the finding: "It is amazing that there is so much to do on just a single layer of graphene even after 20 years of discovery." The results open new questions about whether similar violations of the Wiedemann-Franz Law might occur in other two-dimensional materials, a field that has expanded rapidly since graphene's Nobel Prize-winning isolation in 2004.