2024-02-14 06:10:00
In a field of materials physics, MIT researchers have managed to capture direct images of a fascinating thermal phenomenon known as the “second sound.” This discovery opens a window into the wave behavior of heat in exotic states of matter and could have profound implications for our understanding of superfluids and other related materials.
The wave nature of heat
Unlike the usual dispersion of heat in most materials, where a hot spot gradually dissipates by warming its surroundings, the “second son» describes a behavior where heat travels as a wave, similar to the way sound bounces around in a confined space. This phenomenon has been observed in a very limited number of materials so far.
A unique visualization
THE physicists of WITH not only observed this phenomenon, but also managed to capture direct images of it, revealing how heat can move like a wave and oscillate back and forth, independent of the movement of the material’s physical matter. These images illustrate the pure movement of heat, without the influence of material particles.
Richard Fletcher, assistant professor, compares this phenomenon to a tank of water, half of which is almost boiling.
« You might observe the water appearing completely calm, but suddenly the other side becomes warm, and so on, the heat coming and going, while the water remains perfectly still “, he explains.
The first sound, represented by a simple animation, is an ordinary sound in the form of density waves, in which the normal fluid and the superfluid oscillate together.
The superfluid as a subject of study
The team led by Martin Zwierlein, professor of physics, visualized the “second son” in a superfluide — a special state of matter created when atoms are cooled to extremely low temperatures, causing them to flow like a fluid without any friction. Theorists had predicted that in this superfluid state, heat should also propagate like a wave, although this behavior has not been directly observed until now.
The results, published in the journal Sciencewill help physicists get a more complete picture of how heat moves through superfluids and other related materials, such as superconductors and the neutron stars.
« There are strong connections between our gas cloud and the behavior of electrons in high-temperature superconductors, and even neutrons in ultradense neutron stars », explains Martin Zwierlein.
The second sound is the movement of heat, in which the superfluid and normal fluid “crash into each other,” while leaving the density constant.
A new thermography technique
To isolate and observe the “second son», the team developed a new thermography method, adapted to ultra-low temperatures where the gases do not give off infrared radiation. They used radio frequency to “see” how heat moves through the superfluid, discovering that lithium-6 fermions resonate at different radio frequencies depending on their temperature.
The experiments mark the first time scientists have been able image the second sound directly, and the pure movement of heat in a superfluid quantum gas. The researchers plan to expand their work to more precisely map the behavior of heat in other ultralow gases, and hope that their findings can be extrapolated to predict how heat moves in other highly interactive materials.
« We will now be able to accurately measure thermal conductivity in these systems, and hope to understand and design better systems », concludes Martin Zwierlein.
Illustration caption: For the first time, MIT physicists have captured direct images of the “second sound,” the movement of heat back and forth in a superfluid. These results will allow scientists to better understand heat flows in superconductors and neutron stars. Credit: José-Luis Olivares, MIT
Article : “Thermography of the superfluid transition in a strongly interacting Fermi gas” – DOI: 10.1126/science.adg3430
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