Supersolid
From Freepedia
A supersolid is a spatially ordered superfluid.
| Image:Supersolid phase.png Phase diagram for 4He |
When quantum fluids, like helium-4, are cooled below a certain characteristic temperature, they undergo the superfluid transition and enter a state of zero viscosity.
In helium, it has been proven to be possible to create a supersolid. In this crystalline state, there are holes in the structure which have physical properties just as much as the atoms in the structure do. These holes are created because at tenths of a kelvin, any energy in an atom is enough for it to leave the structure in the same way that it would in the change from solid to liquid or liquid to gas normally. These holes in the structure are mobile, even at 0K. It may seem strange that a gap in the crystal may have any physical properties, but physicists think of these gaps as having energy and mass just as atoms do. This leads to some very bizarre behaviour; the vacancies can move through the solid in synchronicity as if one solid were moving through another. This happens because of the peculiar nature of quantum mechanics. Close to absolute zero, quantum theory says that groups of atoms can lose their individual identities and start behaving like a single, giant atom. Instead of dancing around in a gas or a liquid, these atoms can condense into a single quantum state and start moving in perfect lock-step. This happens because their quantum wave function, the region of space in which a particle is found, spreads out and grows larger than the distance between atoms. Because the vacancies have physical properties, this applies to them too. The effect this has on a solid made up of bosons (no two identical fermions can share the same quantum state) is that once it has been cooled to below 0.4K, and crystallized, the gaps in the structure could condense into one, giant vacancy. This has the implication that just like a ghost passing through a wall, a supersolid made up of vacancies would pass through the rest of the crystal. This effect has been observed by spinning crystallized helium at 0.2K and then stopping it - some has been observed to continue moving through the rest of the crystal that had stopped moving.
In short, a supersolid can pass straight through other supersolids.
