MIT physicists, led by Professor Martin Zwierlein and Assistant Professor Richard Fletcher, have captured the first images of “second sound,” a phenomenon where heat behaves like a wave within a superfluid. This discovery could enhance understanding of heat flow in superconductors and neutron stars. The team used a superfluid state of matter, created by cooling a cloud of atoms to extremely low temperatures, to visualize the heat movement. The research, which also involved Zhenjie Yan, Parth Patel, Biswaroop Mikherjee, and Chris Vale from Swinburne University of Technology, was published in the journal Science.
Discovery of Heat Movement in Superfluids
Physicists at the Massachusetts Institute of Technology (MIT) have made a significant breakthrough in the study of heat movement within superfluids. They have successfully captured direct images of “second sound,” a phenomenon where heat behaves like a wave, moving back and forth within a superfluid. This discovery provides a deeper understanding of heat flow in superconductors and neutron stars.
In most materials, heat tends to scatter, gradually warming its surroundings. However, in certain rare states of matter, heat can behave like a wave, similar to a sound wave bouncing from one end of a room to the other. This wave-like heat movement is what physicists refer to as “second sound.” Until now, signs of second sound have only been observed in a few materials. The new images captured by the MIT team reveal how heat can “slosh” back and forth, independent of a material’s particles.
The Superfluid State and Second Sound
The team, led by Martin Zwierlein, the Thomas A. Frank Professor of Physics, visualized second sound in a superfluid. A superfluid is a special state of matter created when a cloud of atoms is cooled to extremely low temperatures, causing the atoms to flow like a completely friction-free fluid. In this superfluid state, theorists have predicted that heat should also flow like a wave, although this phenomenon had not been directly observed until now.
The researchers used a simple analogy to explain the phenomenon. If one half of a tank of water is nearly boiling, the water might appear calm, but the heat will move back and forth, making one side hot and then the other, while the water remains still.
The Implications of the Discovery
The results of this study, published in the journal Science, will help physicists gain a more comprehensive understanding of how heat moves through superfluids and other related materials, including superconductors and neutron stars. The researchers believe there are strong connections between their findings and the behavior of electrons in high-temperature superconductors, and even neutrons in ultradense neutron stars.
The team’s findings could also have implications for the study of ultracold atoms and fermions, particles that usually avoid each other but can be made to interact and pair up under certain conditions. In this coupled state, fermions can flow in unconventional ways, which the team is exploring.
The Methodology and Future Research
To isolate and observe second sound, the team developed a new method of thermography, a heat-mapping technique. They used radio frequency to “see” how heat moves through the superfluid, as gases do not emit infrared radiation at ultracold temperatures. The researchers found that the lithium-6 fermions resonate at different radio frequencies depending on their temperature. By tracking these resonating fermions over time, they were able to create “movies” that revealed the pure motion of heat.
The researchers plan to extend their work to more precisely map heat’s behavior in other ultracold gases. They believe their findings can be scaled up to predict how heat flows in other strongly interacting materials, such as in high-temperature superconductors, and in neutron stars.
Conclusion
This groundbreaking research marks the first time that scientists have been able to directly image second sound and the pure motion of heat in a superfluid quantum gas. The findings could have significant implications for our understanding of heat flow in superconductors and neutron stars. The researchers hope that their work will lead to the design of better systems and a deeper understanding of these complex phenomena.
