Scientists reveal heat can behave like sound in superfluid

Scientists have revealed that in some exotic states of matter, heat can behave like sound and bounce back and forth. The phenomenon is not new and is known as “second sound.” But the scientists at MIT have for the first time captured the images of the ‘second sound’.

The images show how heat can move like sound waves when generated within a superfluid, a state of matter where atoms flow without any friction. The physicists found that heat and matter can “slosh” against each other, creating oscillations similar to sound waves.

Richard Fletcher, an assistant professor of physics at MIT and a study co-author, was quoted as saying in media reports, “It’s as if you had a tank of water and made one half nearly boiling.”

“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 still,” he added.

Significance

The study, published in Science, can help physicists ascertain how heat behaves in superfluids and other related materials, such as superconductors and neutron stars.

“There are strong connections between our puff of gas, which is a million times thinner than air, and the behaviour of electrons in high-temperature superconductors, and even neutrons in ultradense neutron stars,” says Martin Zwierlein, the Thomas A Frank, Professor of Physics at MIT and the leader of the research team.

“Now we can probe pristinely the temperature response of our system, which teaches us about things that are very difficult to understand or even reach,” he adds.

How was the experiment conducted?

The scientists used a cluster of lithium-6 atoms, fermions that typically repel each other. By chilling the atoms close to absolute zero and implementing a magnetic field, they prompted the atoms to pair up and generate a superfluid.

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Employing a laser beam, they generated a hot spot within the superfluid and employed another laser beam to capture the resulting heat patterns.

Their observations revealed that the heat patterns exhibited periodic motion similar to sound waves but were out of sync with the matter waves, indicating oscillation in opposite directions for heat and matter. This phenomenon, known as second sound, differs from ordinary sound where heat and matter move together.

(With inputs from agencies)