Abstract: In electrically conductive solids, the Wiedemann-Franz law requires the electronic contribution to thermal conductivity to be proportional to electrical conductivity. Violations of the Wiedemann-Franz law are typically an indication of unconventional quasiparticle dynamics, such as inelastic scattering, or hydrodynamic collective motion of charge carriers, typically pronounced only at cryogenic temperatures. We report an order-of-magnitude breakdown of the Wiedemann-Franz law at high temperatures ranging from 240 to 340 kelvin in metallic vanadium dioxide in the vicinity of its metal-insulator transition. Different from previously established mechanisms, the unusually low electronic thermal conductivity is a signature of the absence of quasiparticles in a strongly correlated electron fluid where heat and charge diffuse independently.
Some 2,700 years ago, a massive solar storm bombarded Earth. High-energy particles pinged into the atmosphere, sending a cascade of unstable atoms raining down onto the planet’s surface.
Today, only faint chemical echoes of this ancient collision remain. But according to a study published yesterday in the journal PNAS, scientists have now uncovered these radioactive remnants of the tempest in ice cores from Greenland.
Though this particular storm, which battered Earth sometime around 660 BCE, is one of many recorded, it’s thought to be at least 10 times more powerful than any detected in the past 70 years—suggesting that we might still have incomplete picture of “what the Sun can do.”
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