Superfluids

A detailed Summary of Superfluids

"As we shall see, it is generally believed that the phenomenon of superfluidity is directly connected with the fact that the atoms of helium-4 obey Bose statistics, and that the lambda-transition is due to the onset of the peculiar phenomenon called Bose condensation." (Leggett, 1989)

This is the phenomenon wherein the bosons (a type of particle) making up a substance merge into the lowest energy level, into a shared quantum state. In general, it refers to the tendancy of bosons to occupy the same state. This state, formed when a gas undergoes Bose-Einstein condensation, is called a "Bose-Einstein condensate."

The distinguishing feature of Bose-Einstein condensates is that the many parts that make up the ordered system not only behave as a whole, they become whole. Their identities merge or overlap in such a way that they lose their individuality entirely. A good analogy would be the many voices of a choir, merging to become 'one voice' at certain levels of harmony.

The phenomenon of superfluidity was discovered in 1937 by a Russian physicist, Peter Kapitza, and then studied independently in 1938 by John Frank Allen, a British physicist, and his coworkers. I

Superfluidity is a state of matter characterized by the complete absence of viscosity, or resistance to flow. This term is used primarily when involving liquid helium at very low temperatures. It was found that liquid helium (4He), when cooled below 2.17K (-271O C or -456 O F, could flow with no difficulty through extremely small holes, which liquid helium at a higher temperature cannot do. It was also noted that the walls of its container were somehow coated with a thin film of helium (approximately 100 atoms thick). This film flowed against gravity up and over the rim of the container

When the temperature is dropped still lower, it was found that the stable isotope helium-3 is formed. This liquid exhibits superfluid characteristics, but only at temperatures lower than 0.0025 K. Nuclei of helium-3 contain two protons and one neutron, rather than the two protons and two neutrons found in the more common isotope, helium-4. Superfluid helium-4 forms at approximately 2.17 K. This superfluid moves without friction, squeezes through impossibly small holes, and it can even flow uphill. Superfluid helium-3 can do all these things, however not so spectacularly. The weird thing about helium-3 is that it can have different properties in different directions, similar to the well-defined grain in a piece of wood.

Bosons follow Bose-Einstein statistics but fermions can have at most one particle in each one-particle quantum state. Fermions cannot undergo Bose-Einstein condensation, but the nuclei in helium-3 can 'disguise' itself as bosons by pairing up to form Cooper pairs, which behave as bosons. When this happens however, the spin value is one, rather than the zero spin on helium-4. This is the key difference and is used to understand superfluid helium-3. As a result of this, all the spins of composite particles in superfluid helium-3 can be lined up by placing a magnetic field around the liquid. This alignment of spins can explain why properties of superfluid helium-3 are different in different orientations. For example, sound travels through it at different speeds in different directions, and it will flow faster in one direction than in another.

Some common words found in the essay are:
Helium II, Prize Physics, HELIUM Superfluidity, SUPERFLUIDS Helium, CONCLUSION Superfluidity, BOSE-EINSTEIN CONDENSATION, , Cornell University, Tilley Tilley, Allen British, superfluid helium-3, liquid helium, low temperature, bose-einstein condensation, superfluidity helium-3, superfluid helium, helium ii, phase transitions, low temperatures, fur physik germany, leggett 1989, define temperature scales, zeitschrift fur physik,

Approximate Word count = 1536
Approximate Pages = 6 (250 words per page double spaced)

Category: Science