* In a solid, the atoms are fixed in place and vibrate about their equilibrium positions.
* In a superfluid, the atoms are not fixed in place and can flow without any resistance.
A supersolid is a solid that also exhibits superfluid properties, meaning that it has non-zero rigidity, but also supports the flow of matter without dissipation or friction.
Superfluidity in solids was predicted theoretically in 1969 by Anthony Leggett, who suggested that this new phase could occur in crystals with strong atomic interactions, where quantum fluctuations can lead to delocalization of some atoms and the formation of a superfluid component.
The experimental observation of supersolidity remained elusive for decades, and its very existence was controversial.
In 2017, a team of researchers at the University of California, Berkeley, led by physicist David Ceperley, reported the observation of supersolidity in a crystal of solid helium-4. The researchers used a novel experimental technique to measure the torsional oscillations of a helium-4 crystal and found that the crystal's rigidity decreased at low temperatures, while its ability to flow increased. This behavior is consistent with the theoretical predictions for a supersolid.
The observation of supersolidity in solid helium-4 has opened up new avenues of research in condensed matter physics and quantum mechanics. Supersolids are expected to exhibit a variety of interesting properties, such as the ability to conduct heat and electricity without any resistance, and the ability to support the flow of matter without any friction. These properties could have a wide range of applications, including the development of new superconductors, superfluids, and other advanced materials.
