Superconductors
Superconductors are materials which have zero electrical resistance, and therefore perfect conductivity. They also exclude all magnetic fields from their interior, a phenomenon known as the Meissner effect or perfect diamagnetism. Superconducting magnets are used as electromagnets in magnetic resonance imaging machines.
The phenomenon of superconductivity was discovered in 1911, and for 75 years was only known in some metals and metallic alloys at temperatures below 30 K. In 1986 so-called high-temperature superconductivity was discovered in certain ceramic oxides, and has now been observed in temperatures as high as 164 K. [13]
Superfluids
Close to absolute zero, some liquids form a second liquid state described as superfluid because it has zero viscosity or infinite fluidity. This was discovered in 1937 for helium which forms a superfluid below the lambda temperature of 2.17 K. In this state it will attempt to 'climb' out of its container.[14]. It also has infinite thermal conductivity so that no temperature gradient can form in a superfluid.
These properties are explained by the theory that the common isotope helium-4 forms a Bose–Einstein condensate (see next section) in the superfluid state. More recently, Fermionic condensate superfluids have been formed at even lower temperatures by the rare isotope helium-3 and by lithium-6.[15]
Bose-Einstein condensates
In 1924, Albert Einstein and Satyendra Nath Bose predicted the "Bose-Einstein condensate," sometimes referred to as the fifth state of matter.
In the gas phase, the Bose-Einstein condensate remained an unverified theoretical prediction for many years. Finally in 1995, Wolfgang Ketterle and his team of graduate students produced such a condensate experimentally. A Bose-Einstein condensate is "colder" than a solid. It may occur when atoms have very similar (or the same) quantum levels, at temperatures very close to absolute zero (-273 °C).
Rydberg molecules
One of the metastable states of strongly non-ideal plasma is Rydberg matter, which forms upon condensation of excited atoms. These atoms can also turn into ions and electrons if they reach a certain temperature. In April 2009, Nature [16] reported the creation of Rydberg molecules from a Rydberg atom and a groundstate atom by University of Stuttgart researchers, confirming University of Colorado at Boulder physicist Chris Greene's hypothesis that such a state of matter could exist [17]. The experiment was performed using ultracold rubidium atoms.
High-energy states
Plasma (ionized gas)
Plasmas or ionized gases can exist at temperatures starting at several thousand degrees C. Two examples of plasma are the charged air produced by lightning, and a star such as our own sun.
As a gas is heated, electrons begin to leave the atoms, resulting in the presence of free electrons, which are not bound to an atom or molecule, and ions, which are chemical species that contain unequal number of electrons and protons, and therefore possess an electrical charge. The free electric charges make the plasma electrically conductive so that it responds strongly to electromagnetic fields. At very high temperatures, such as those present in stars, it is assumed that essentially all electrons are "free," and that a very high-energy plasma is essentially bare nuclei swimming in a sea of electrons. Plasma is believed to be the most common state of matter in the universe.
A plasma can be considered as a gas of highly ionized particles, but the powerful interionic forces lead to distinctly different properties, so that it is usually considered as a different phase or state of matter.
Quark-gluon plasma
This is a state of matter discovered at the CERN in 2000[18], in which the quarks that would normally make up protons and neutrons are freed and can be observed individually, similar to splitting molecules into atoms. This state of matter allows scientists to observe the properties of individual quarks, and not just theorize. See also Strangeness production.
Other proposed states
Degenerate matter
Under extremely high pressure, ordinary matter undergoes a transition to a series of exotic states of matter collectively known as degenerate matter. These are of great interest to astrophysics, because these high-pressure conditions are believed to exist inside stars that have used up their nuclear fusion "fuel", such as white dwarves and neutron stars.
Supersolid
A supersolid is a spatially ordered material (that is, a solid or crystal) with superfluid properties. A supersolid is a solid, but exhibits so many other properties that many argue it is another state of matter.[19]
String-net liquid
When in a normal solid state, the atoms of matter align themselves in a grid pattern, so that the spin of any electron is the opposite of the spin of all electrons touching it. But in a string-net liquid, atoms are arranged in some pattern which would require some electrons to have neighbors with the same spin. This gives rise to some curious properties, as well as supporting some unusual proposals about the fundamental conditions of the universe itself.
Superglass
A superglass is a phase of matter which is characterized at the same time by superfluidity and a frozen amorphous structure.
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