when something gets warmed up, heat tends to spread outward before eventually dissipating. But things are a little different in the world of superfluid quantum gas.
For the first time, MIT scientists have successfully imaged how heat actually travels in a wave, known as a “second sound,” through this exotic fluid.
Understanding this dynamic could help answer questions about high-temperature superconductors and neutron stars.
In the world of average, everyday materials, heat tends to spread out from a localized source. Drop a burning coal into a pot of water, and that liquid will slowly rise in temperature before its heat eventually dissipates. But the world is full of rare, exotic materials that don’t exactly play by these thermal rules.
Instead of spreading out as one would expect, these superfluid quantum gasses “slosh” heat side to side—it essentially propagates as a wave. Scientists call this behavior a material’s “second sound” (the first being ordinary sound via a density wave). Although this phenomenon has been observed before, it’s never been imaged. But recently, scientists at the Massachusetts Institute of Technology (MIT) were finally able to capture this movement of pure heat by developing a new method of thermography (a.k.a. heat-mapping).
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The results of this study were published in the journal Science, and in an university press release highlighting the achievement, MIT assistant professor and co-author Richard Fletcher continued the boiling pot analogy to describe the inherent strangeness of “second sound” in these exotic superfluids
https://www.popularmechanics.com/science/a64093045/second-wave-superfluid-existence/
In superfluids, heat propagates like a wave in a phenomenon dubbed “second sound. ” However, observing this propagation directly is tricky. Yan et al. used a quantum gas of strongly interacting fermionic lithium atoms held in a box potential to visualize second sound.
The researchers used radiofrequency spectroscopy to map out local changes to the temperature.
Above the superfluid transition, heat propagated diffusively, but below the transition, wave-like propagation characteristic of second sound was observed. —Jelena Stajic
https://www.science.org/doi/10.1126/science.adg3430
MIT physicists capture the first sounds of heat “sloshing” in a superfluid
The results will expand scientists’ understanding of heat flow in superconductors and neutron stars.
February 8, 2024
In most materials, heat prefers to scatter. If left alone, a hotspot will gradually fade as it warms its surroundings.
But in rare states of matter, heat can behave as a wave, moving back and forth somewhat like a sound wave that bounces from one end of a room to the other. In fact, this wave-like heat is what physicists call “second sound.”
Signs of second sound have been observed in only a handful of materials. Now MIT physicists have captured direct images of second sound for the first time
The new images reveal how heat can move like a wave, and “slosh” back and forth, even as a material’s physical matter may move in an entirely different way. The images capture the pure movement of heat, independent of a material’s particles.
“It’s as if you had a tank of water and made one half nearly boiling,” Assistant Professor Richard Fletcher offers as analogy. “If you then watched, the water itself might look totally calm, but suddenly the other side is hot, and then the other side is hot, and the heat goes back and forth, while the water looks totally still.”
Led by Martin Zwierlein, the Thomas A Frank Professor of Physics, the team visualized second sound in a superfluid — a special state of matter that is created when a cloud of atoms is cooled to extremely low temperatures, at which point the atoms begin to flow like a completely friction-free fluid. In this superfluid state, theorists have predicted that heat should also flow like a wave, though scientists had not been able to directly observe the phenomenon until now.
https://news.mit.edu/2024/mit-physicists-capture-first-sounds-heat-sloshing-superfluid-0208
h/t Digital mix guy Kirk Spock