For decades, the Wiedemann-Franz law stood as a reliable rule in condensed matter physics.
This principle holds that a material’s ability to conduct electricity should rise and fall in lockstep with its ability to conduct heat.
A team of researchers from the Indian Institute of Science and the National Institute for Materials Science in Japan has now documented a dramatic violation of this long-standing tenet.
Their experiments on graphene, a single layer of carbon atoms, show that electrical conductivity and thermal conductivity can move in opposite directions rather than together.
The scientists created exceptionally clean graphene samples to eliminate interference from atomic defects and impurities.
They then carefully measured both electrical and thermal conduction across a range of conditions. What emerged was a striking contradiction to established physics.
As electrical conductivity increased, thermal conductivity dropped, and the reverse also occurred.
At low temperatures, the observed deviation from the Wiedemann-Franz law exceeded a factor of 200.
This separation between charge flow and heat flow is not a minor anomaly but a fundamental breakdown of a rule that has guided physicists for more than a century.
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