A Massachusetts Institute of Technology (MIT) team has visually documented the ‘second sound,’ a revolutionary wave-like heat movement in superfluids, challenging conventional understanding of thermal dynamics.
For the first time, scientists at the Massachusetts Institute of Technology (MIT) have directly captured images of a phenomenon known as “second sound,” offering new insights into the unique ways heat can behave in certain states of matter. Unlike in conventional materials where heat spreads out, in rare instances, it can move back and forth like a wave, a behaviour previously observed in only a few materials.
The researchers visualized this wave-like heat movement in a superfluid, a state of matter achieved when atoms are cooled to extremely low temperatures, allowing them to flow without friction. This superfluid state enables heat to propagate wave-likely, independent of the material’s physical particles, a concept theoretically predicted but not visually confirmed until now.
Using a new thermography technique, the team was able to capture the movement of heat waves sloshing back and forth, revealing the heat’s pure motion. This method, based on radio frequency rather than infrared radiation (which is ineffective at ultracold temperatures), allowed the researchers to “see” how heat moved through the superfluid by detecting the varying resonances of the fermionic lithium-6 atoms at different temperatures.
This discovery confirms the existence of a second sound and enhances understanding of superfluidity and its characteristics. The phenomenon of second sound was first proposed in the context of superfluidity by physicist László Tisza in 1938 and later named by Lev Landau. It suggests that superfluids contain both a normal, viscous fluid and a friction-free superfluid component, allowing for two types of sound waves: ordinary density waves and temperature waves, or second sound.
The implications of this study extend beyond the confines of superfluids, potentially impacting our understanding of high-temperature superconductors, neutron stars, and other strongly interacting materials. The team claims their approach to visualizing heat movement opens new avenues for exploring thermal conductivity in these complex systems, hoping to develop better materials and gain deeper insights into their behaviours.
This research sheds light on fundamental physical principles and promises to inform the design and understanding of future technological applications.