Supersolid
Introduction
A supersolid is a spatially ordered material with superfluid properties. Superfluidity is a state of matter in which matter behaves like a fluid with zero viscosity; where it appears to exhibit the ability to self-propel and travel in a way that defies the forces of gravity and surface tension. While a supersolid is a theoretical state of matter proposed by physicists, no solid materials with such properties have been found yet.
History
The concept of a supersolid was first introduced by Russian physicist Andrei Andreev and British physicist David J. Thouless in 1969. They proposed that a solid helium-4, a bosonic isotope of helium, could potentially exhibit this phase due to its quantum mechanical nature. This idea was based on the known superfluid properties of liquid helium-4, and the understanding that quantum mechanics can lead to a blurring of the distinct states of liquid and solid in certain systems.
Theoretical Properties
According to the theory, a supersolid is a solid that also exhibits properties of superfluids. This means that it would have a crystal lattice structure like a solid, but also be able to flow without friction, like a superfluid. This is due to a phenomenon known as Bose-Einstein condensate, where particles at very low temperatures can occupy the same quantum state, leading to quantum phenomena on macroscopic scales.
The properties of a supersolid would be quite unusual. For example, if a supersolid were rotated, parts of it would continue to remain stationary due to the superfluid properties. This is known as the "non-classical rotational inertia" and is one of the key signatures of superfluidity.
Experimental Evidence
In 2004, a team of researchers led by Moses Chan at Pennsylvania State University reported that they had observed the supersolid phase in solid helium-4. They had cooled the helium-4 to temperatures near absolute zero, and then measured its moment of inertia. They found that the moment of inertia decreased at low temperatures, which they interpreted as evidence for the supersolid phase.
However, subsequent experiments by other groups could not reproduce these results, and it was found that the observed behavior could be explained by defects in the crystal lattice of the solid helium-4. This led to a consensus in the scientific community that the original experiments did not provide evidence for the existence of a supersolid phase.
Current Research
Despite the setbacks, research into supersolids continues. Theoretical physicists are still interested in the possibility of this exotic state of matter, and experimentalists are searching for new systems in which to look for it. One promising area of research is in the field of ultracold atomic gases, where it is possible to create and manipulate states of matter that are not accessible in more traditional solid materials.
Conclusion
The supersolid is a fascinating theoretical state of matter that merges the properties of solids and superfluids. While experimental evidence for supersolids is currently lacking, the search for this exotic state of matter continues. If found, it could provide new insights into the nature of matter and the quantum world.