14 DAY TRIAL // Most of the studies conducted in the last decade, for understanding the nature of liquids and solids, involved dilute atomic gases at extremely low temperatures, such as helium-4 a isotope of helium that has atomic boson properties, meaning its cumulated spin is an integer number. Helium-3 didn't escape the physicists attention either, since it is considered an atomic fermion with half-integer number, forbidden from collapsing into a Bose-Einstein condensate by Pauli's exclusion principle, which states that no two identical fermion particles can occupy the same quantum state at the same time.
On the other hand, German physicists claim they have designed a new cooling method by mixing fermion atom species with boson atom species, which was later removed from the mix. Fermionic atoms can be manipulated into pairing up with each other, in order to form a boson atom species with the help of magnetic fields and laser systems.
The so-called Fermi-Fermi Bose-Einstein condensate presents special properties due to the fermionic sub-atomic particles, mostly electrons that pair in order to reduce the electrical resistance of the mixture. Such ultracold gases could determine interactions inside the system, which would give the BEC condensate properties similar to those of the high-temperature superconductors.
The first true breakthrough came in 2005, when MIT researchers created for the first time a Bose-Einstein condensate that implied the use of atoms with different fermionic states, meaning that they used atoms with different spin. Now however, physicists have been able to take the studies one step higher, by using lithium-6 and potassium-40 atoms to create a Fermi-Fermi mixture.
Due to the unique properties of the atomic boson species, the German team had no choice than to use evaporative cooling in order to bring the fermionic gas to extremely low temperature, since they had already solved this problem in a similar experiment using rubidium-87 bosonic gas.
Because the rubidium-87 is so efficient when it comes to evaporative cooling to lower the temperature of the potassium-40, this triggers a less cooling effect on the lithium-6 gas, mainly due to the fact that the lithium atoms are much smaller and have less chances of losing energy through collision processes with the rubidium-87 gas. The lithium-6 cooling problem can be solved relatively easy, by lowering its temperature with the help of the potassium-40 gas, which has atomic size much close to that of lithium-6. As soon as the whole BEC mixture is cooled, the catalyst substance namely rubidium-87 can be extracted from the system to leave it at a temperature lower than one microKelvin.
Bose-Einstein condensates, especially Fermi-Fermi systems, are thought to have the abilities to provide insight into the fundamental quantum interactions which take place inside matter, or could be used to create heteronuclear systems with the help of lithium and potassium atoms that reveal interactions which are thought to be responsible for determining some types of magnetism, pairing in superconductors and superfluids.