Bose-Einstein and Fermionic Condensates
The fermionic condensate is a new phase of matter, first created on December 16, 2003 by physicist Deborah S. Jin. It is the sixth known phase of matter, and is related to the Bose-Einstein condensate, which was first created in 1995. The five other phases of matter are gases, solids, liquids, plasmas and Bose-Einstein condensates.
Bose-Einstein condensates are formed at low temperatures when a significant number of bosons collapse into the same quantum state. A similar condensate that uses fermions instead of bosons is known as a fermionic condensate. Such a condensate is far more difficult to achieve because the Pauli exclusion principle prohibits two or more fermions from occupying the same quantum state.
In 1957, John Bardeen, Leon Cooper and Robert Schrieffer proposed that electrons, a type of fermion, could pair-up to form what are now known as Cooper pairs - such pairs essentially act like bosons. If a similar sort of pairing were possible amongst fermionic atoms then the formation of a fermionic condensate might be possible. However until recently many believed that the temperature required for such a pairing would be too cold to achieve.
In 2001, physicist Murray Holland of the Joint Institute for Laboratory Astrophysics (JILA) speculated that fermionic atoms could be coaxed into pairing up at higher temperatures by subjecting them to a magnetic field. In 2003, Deborah Jin of the same institute (JILA) and Rudolf Grimm of the University of Innsbruck were able to coax fermionic atoms into bonding to form molecular bosons and thus able to form a Bose-Einstein condensate but not a fermionic condensate.
On December 16 2003, Deborah Jin observed the pairing and formation of a fermionic condensate among fermionic atoms for the very first time. The experiment involved 500,000 Potassium-40 atoms cooled to a temperature of 5 × 10-8 kelvin with a time-varying magnetic field applied to them. The findings were published in the online edition of Physical Review Letters on January 24, 2004.
The Helium Superfluids and the Condensates
Superfluidity is an unusual state characterised by the complete absence of viscosity. Superfluids exist only at low temperatures and possess a number of strange characteristics. For example, when placed in an open container a superfluid will gradually flow up and over the sides of the container due to film flow. All Bose-Einstein and fermionic condensates are superfluids however there are also two Helium-based superfluids. These Helium-based superfluids were created prior to Bose-Einstein and fermionic condensates and are noteworthy because of the similarities they share with Bose-Einstein and fermionic condensates.
In 1938, Pyotr Kapitsa, John Allen and Don Misener discovered superfluidity amongst Helium-4 atoms (which are bosons) by cooling them to a temperature of less than 2.17 kelvin. Like a Bose-Einstein condensate the Helium-4 superfluid arose because of the collapse of a significant number of bosons into the same quantum state. However the Helium-4 superfluid was formed from liquid Helium-4 as opposed to a Bose gas and therefore could not be considered a Bose-Einstein condensate.
In 1971, Douglas Osheroff, David Lee and Robert Richardson discovered superfluidity amongst Helium-3 atoms (which are fermions) by cooling them to a temperature of less than 2.6 millikelvin. Like a fermionic condensate this Helium-3 superfluid arose because pairing between the fermions allowed them to collapse into a single quantum state. However the Helium-3 superfluid was formed from liquid Helium-3 as opposed to a fermi gas and therefore could not be considered a fermionic condensate.
Superconductivity is a phenomenon characterized by the complete absence of electrical resistance. Currently superconductors exist only at low temperatures however an affordable room temperature superconductor would revolutionize the electrical and electronic industries allowing for more efficient electric power generation and transmission as well as more effective electromagnets.
Conventional superconductivity is currently best explained by BCS theory. This theory suggests that conventional superconductivity is dependent on the Cooper pairing of electrons. As mentioned before, a similar pairing mechanism is necessary in order to form fermionic condensates. However the pairing mechanism involved in Jin's fermionic condensate is much stronger than that in the Cooper pairing of electrons. In this context, Jin notes that “the strength of pairing in our fermionic condensate, adjusted for mass and density would correspond to a room temperature superconductor."
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