Difference between revisions of "Superfluidity" - New World Encyclopedia
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| − | [[Image:helium-II-creep.svg|thumb|right| | + | {{Claimed}} |
| − | '''Superfluidity''' is a [[phase (matter)|phase of matter]] or description of [[heat capacity]] in which [[superconductivity]] and "unusual" effects are observed when [[liquids]], typically of [[helium-4]] or [[hydrogen]], overcome [[friction]] by surface interaction when at a stage, known as "[[lambda point]]" | + | [[Image:helium-II-creep.svg|thumb|right|230px|Helium II will "creep" along surfaces to find its own level—after a short while, the levels in the two containers will equalize. The helium film (called a [[Rollin film]]) also covers the interior of the larger container; if it were not sealed, the helium II would creep out and escape.]] |
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| + | '''Superfluidity''' is a [[phase (matter)|phase of matter]] or description of [[heat capacity]] in which [[superconductivity]] and "unusual" effects are observed when [[liquids]], typically of [[helium-4]] or [[hydrogen]], overcome [[friction]] by surface interaction when at a stage, known as "[[lambda point]]," at which the liquid's [[viscosity]] becomes [[zero]]. Also known as a major facet in the study of [[quantum hydrodynamics]], it was discovered by [[Pyotr Leonidovich Kapitsa]], [[John F. Allen]], and [[Don Misener]] in 1937 and has been described through [[Phenomenology (science)|phenomenological]] and microscopic theories. | ||
==Background== | ==Background== | ||
Although the phenomenologies of the superfluid states of helium-4 and [[helium-3]] are very similar, the microscopic details of the transitions are very different. Helium-4 [[atoms]] are [[boson]]s, and their superfluidity can be understood in terms of the [[Bose statistics]] that they obey. Specifically, the super fluidity of helium-4 can be regarded as a consequence of [[Bose-Einstein condensate|Bose-Einstein condensation]] in an interacting system. On the other hand, helium-3 atoms are [[fermion]]s, and the superfluid transition in this system is described by a generalization of the [[BCS theory]] of superconductivity. In it, [[Cooper pair]]ing takes place between atoms rather than [[electrons]], and the attractive interaction between them is mediated by [[spin]] fluctuations rather than [[phonon]]s. See [[fermion condensate]]. A unified description of superconductivity and super fluidity is possible in terms of [[spontaneous symmetry breaking|gauge symmetry breaking]]. | Although the phenomenologies of the superfluid states of helium-4 and [[helium-3]] are very similar, the microscopic details of the transitions are very different. Helium-4 [[atoms]] are [[boson]]s, and their superfluidity can be understood in terms of the [[Bose statistics]] that they obey. Specifically, the super fluidity of helium-4 can be regarded as a consequence of [[Bose-Einstein condensate|Bose-Einstein condensation]] in an interacting system. On the other hand, helium-3 atoms are [[fermion]]s, and the superfluid transition in this system is described by a generalization of the [[BCS theory]] of superconductivity. In it, [[Cooper pair]]ing takes place between atoms rather than [[electrons]], and the attractive interaction between them is mediated by [[spin]] fluctuations rather than [[phonon]]s. See [[fermion condensate]]. A unified description of superconductivity and super fluidity is possible in terms of [[spontaneous symmetry breaking|gauge symmetry breaking]]. | ||
| − | Superfluids, such as supercooled helium-4, exhibit many unusual properties. A superfluid acts as if it were a mixture of a normal component, with all the properties associated with normal fluid, and a superfluid component. The superfluid component has zero [[viscosity]], zero [[entropy]], and infinite [[thermal conductivity]]. (It is thus impossible to set up a [[temperature gradient]] in a superfluid, much as it is impossible to set up a [[voltage]] difference in a superconductor.) One of the most spectacular results of these properties is known as the [[thermomechanical]] or "fountain effect" | + | Superfluids, such as supercooled helium-4, exhibit many unusual properties. A superfluid acts as if it were a mixture of a normal component, with all the properties associated with normal fluid, and a superfluid component. The superfluid component has zero [[viscosity]], zero [[entropy]], and infinite [[thermal conductivity]]. (It is thus impossible to set up a [[temperature gradient]] in a superfluid, much as it is impossible to set up a [[voltage]] difference in a superconductor.) One of the most spectacular results of these properties is known as the [[thermomechanical]] or "fountain effect." If a [[capillary tube]] is placed into a bath of superfluid helium and then heated, even by shining a [[light]] on it, the superfluid helium will flow up through the tube and out the top as a result of the [[Clausius-Clapeyron relation]]. A second unusual effect is that superfluid helium can form a layer, a single atom thick, up the sides of any container in which it is placed. |
A more fundamental property than the disappearance of viscosity becomes visible if superfluid is placed in a rotating container. Instead of rotating uniformly with the container, the rotating state consists of [[Quantum vortex|quantized vortices]]. That is, when the container is rotated at [[speed]] below the first critical [[velocity]] (related to the [[quantum numbers]] for the [[element]] in question) the liquid remains perfectly stationary. Once the first critical velocity is reached, the superfluid will very quickly begin spinning at the critical speed. The speed is quantized - i.e. it can only spin at certain speeds. | A more fundamental property than the disappearance of viscosity becomes visible if superfluid is placed in a rotating container. Instead of rotating uniformly with the container, the rotating state consists of [[Quantum vortex|quantized vortices]]. That is, when the container is rotated at [[speed]] below the first critical [[velocity]] (related to the [[quantum numbers]] for the [[element]] in question) the liquid remains perfectly stationary. Once the first critical velocity is reached, the superfluid will very quickly begin spinning at the critical speed. The speed is quantized - i.e. it can only spin at certain speeds. | ||
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Recently, superfluids have been used to trap and slow the [[speed of light]]. In an experiment, performed by [[Lene Hau]], light was passed through a superfluid and found to be slowed to 17 meters per second (normally ~ 300,000,000 meters per second). | Recently, superfluids have been used to trap and slow the [[speed of light]]. In an experiment, performed by [[Lene Hau]], light was passed through a superfluid and found to be slowed to 17 meters per second (normally ~ 300,000,000 meters per second). | ||
| − | The [[Infrared]] [[Astronomical]] [[Satellite]] ([[IRAS]]), launched in January | + | The [[Infrared]] [[Astronomical]] [[Satellite]] ([[IRAS]]), launched in January 1983 to gather infrared [[data]] was cooled by 720 litres of superfluid helium, maintaining a [[temperature]] of 1.6K. |
==Recent discoveries== | ==Recent discoveries== | ||
[[Physicists]] have recently been able to create a Fermionic condensate from pairs of ultra-cold fermionic atoms. Under certain conditions, fermion pairs form [[diatomic]] molecules and undergo [[Bose–Einstein condensate|Bose–Einstein condensation]]. At the other limit, the fermions (most notably superconducting electrons) form [[Cooper pairs]] which also exhibit superfluidity. This recent work with ultra-cold atomic gases has allowed [[scientists]] to study the region in between these two extremes, known as the [[BEC-BCS crossover]]. | [[Physicists]] have recently been able to create a Fermionic condensate from pairs of ultra-cold fermionic atoms. Under certain conditions, fermion pairs form [[diatomic]] molecules and undergo [[Bose–Einstein condensate|Bose–Einstein condensation]]. At the other limit, the fermions (most notably superconducting electrons) form [[Cooper pairs]] which also exhibit superfluidity. This recent work with ultra-cold atomic gases has allowed [[scientists]] to study the region in between these two extremes, known as the [[BEC-BCS crossover]]. | ||
| − | Additionally, [[supersolid|super''solids'']] might have also been discovered, in | + | Additionally, [[supersolid|super''solids'']] might have also been discovered, in 2004, by physicists at [[Penn State University]]. When helium-4 is cooled, below about 200 mK under high pressures, a [[fraction]] (~1%) of the [[solid]] appears to become superfluid [http://www.phys.psu.edu/~chan/index_files/Page526.htm]. |
==Books== | ==Books== | ||
| − | * [[Hagen Kleinert]], ''Gauge Fields in Condensed Matter'', Vol. I, "SUPERFLOW AND VORTEX LINES" | + | * [[Hagen Kleinert]], ''Gauge Fields in Condensed Matter'', Vol. I, "SUPERFLOW AND VORTEX LINES," pp. 1–742, [http://www.worldscibooks.com/physics/0356.htm World Scientific (Singapore, 1989)]; Paperback ISBN 9971-5-0210-0 (also available online [http://www.physik.fu-berlin.de/~kleinert/kleiner_reb1/contents1.html here]) |
==See also== | ==See also== | ||
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Revision as of 19:43, 21 June 2007
Superfluidity is a phase of matter or description of heat capacity in which superconductivity and "unusual" effects are observed when liquids, typically of helium-4 or hydrogen, overcome friction by surface interaction when at a stage, known as "lambda point," at which the liquid's viscosity becomes zero. Also known as a major facet in the study of quantum hydrodynamics, it was discovered by Pyotr Leonidovich Kapitsa, John F. Allen, and Don Misener in 1937 and has been described through phenomenological and microscopic theories.
Background
Although the phenomenologies of the superfluid states of helium-4 and helium-3 are very similar, the microscopic details of the transitions are very different. Helium-4 atoms are bosons, and their superfluidity can be understood in terms of the Bose statistics that they obey. Specifically, the super fluidity of helium-4 can be regarded as a consequence of Bose-Einstein condensation in an interacting system. On the other hand, helium-3 atoms are fermions, and the superfluid transition in this system is described by a generalization of the BCS theory of superconductivity. In it, Cooper pairing takes place between atoms rather than electrons, and the attractive interaction between them is mediated by spin fluctuations rather than phonons. See fermion condensate. A unified description of superconductivity and super fluidity is possible in terms of gauge symmetry breaking.
Superfluids, such as supercooled helium-4, exhibit many unusual properties. A superfluid acts as if it were a mixture of a normal component, with all the properties associated with normal fluid, and a superfluid component. The superfluid component has zero viscosity, zero entropy, and infinite thermal conductivity. (It is thus impossible to set up a temperature gradient in a superfluid, much as it is impossible to set up a voltage difference in a superconductor.) One of the most spectacular results of these properties is known as the thermomechanical or "fountain effect." If a capillary tube is placed into a bath of superfluid helium and then heated, even by shining a light on it, the superfluid helium will flow up through the tube and out the top as a result of the Clausius-Clapeyron relation. A second unusual effect is that superfluid helium can form a layer, a single atom thick, up the sides of any container in which it is placed.
A more fundamental property than the disappearance of viscosity becomes visible if superfluid is placed in a rotating container. Instead of rotating uniformly with the container, the rotating state consists of quantized vortices. That is, when the container is rotated at speed below the first critical velocity (related to the quantum numbers for the element in question) the liquid remains perfectly stationary. Once the first critical velocity is reached, the superfluid will very quickly begin spinning at the critical speed. The speed is quantized - i.e. it can only spin at certain speeds.
Applications
Recently in the field of chemistry, superfluid helium-4 has been successfully used in spectroscopic techniques, as a quantum solvent. Referred to as Superfluid Helium Droplet Spectroscopy (SHeDS), it is of great interest in studies of gas molecules, as a single molecule solvated in a superfluid medium allows a molecule to have effective rotational freedom - allowing it to behave exactly as it would in the "gas" phase.
Superfluids are also used in high-precision devices, such as gyroscopes, which allow the measurement of some theoretically predicted gravitational effects (for an example see the Gravity Probe B article).
Recently, superfluids have been used to trap and slow the speed of light. In an experiment, performed by Lene Hau, light was passed through a superfluid and found to be slowed to 17 meters per second (normally ~ 300,000,000 meters per second).
The Infrared Astronomical Satellite (IRAS), launched in January 1983 to gather infrared data was cooled by 720 litres of superfluid helium, maintaining a temperature of 1.6K.
Recent discoveries
Physicists have recently been able to create a Fermionic condensate from pairs of ultra-cold fermionic atoms. Under certain conditions, fermion pairs form diatomic molecules and undergo Bose–Einstein condensation. At the other limit, the fermions (most notably superconducting electrons) form Cooper pairs which also exhibit superfluidity. This recent work with ultra-cold atomic gases has allowed scientists to study the region in between these two extremes, known as the BEC-BCS crossover.
Additionally, supersolids might have also been discovered, in 2004, by physicists at Penn State University. When helium-4 is cooled, below about 200 mK under high pressures, a fraction (~1%) of the solid appears to become superfluid [1].
Books
- Hagen Kleinert, Gauge Fields in Condensed Matter, Vol. I, "SUPERFLOW AND VORTEX LINES," pp. 1–742, World Scientific (Singapore, 1989); Paperback ISBN 9971-5-0210-0 (also available online here)
See also
- Superdiamagnetism
- Bose-Einstein condensate
- Superconductivity
- Quantum vortex
- Supersolid
- superfluid film
External links
- Superfluid phases of helium
- Lancaster University, Ultra Low Temperature Physics - Superfluid helium-3 research group.
- http://www.aip.org/png/html/helium3.htm
- http://www.aip.org/pt/vol-54/iss-2/p31.html
- http://web.mit.edu/newsoffice/2005/matter.html
- http://physicsweb.org/articles/world/11/6/3/1
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| Solid | Liquid | Gas | Plasma Colloid | Supercritical fluid | Superfluid | Supersolid | Degenerate matter | Quark-gluon plasma | Fermionic condensate | Bose-Einstein condensate | Strange matter melting point | boiling point | triple point | critical point | equation of state | cooling curve |
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