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Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic flux fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source.
Unconventional superconductors are materials that display superconductivity which does not conform to either the conventional BCS theory or Nikolay Bogolyubov's theory or its extensions.
High-temperature superconductors are defined as materials that behave as superconductors at temperatures above 77 K, the boiling point of liquid nitrogen. The adjective "high temperature" is only in respect to previously known superconductors, which function at even colder temperatures close to absolute zero. In absolute terms, these "high temperatures" are still far below ambient, and therefore require cooling. The first high-temperature superconductor was discovered in 1986, by IBM researchers Bednorz and Müller, who were awarded the Nobel Prize in Physics in 1987 "for their important break-through in the discovery of superconductivity in ceramic materials". Most high-Tc materials are type-II superconductors.
Metallic hydrogen is a phase of hydrogen in which it behaves like an electrical conductor. This phase was predicted in 1935 on theoretical grounds by Eugene Wigner and Hillard Bell Huntington.
A room-temperature superconductor is a material that is capable of exhibiting superconductivity at operating temperatures above 0 °C, that is, temperatures that can be reached and easily maintained in an everyday environment. As of 2020, the material with the highest accepted superconducting temperature is an extremely pressurized carbonaceous sulfur hydride with a critical transition temperature of +15 °C at 267 GPa. On 22 September 2022, the original article reporting superconductivity in the carbonaceous sulfur hydride material was retracted by Nature journal editorial board due to a non standard, user-defined data analysis, calling into question the scientific validity of the claim.
Solid oxygen forms at normal atmospheric pressure at a temperature below 54.36 K (−218.79 °C, −361.82 °F). Solid oxygen O2, like liquid oxygen, is a clear substance with a light sky-blue color caused by absorption in the red part of the visible light spectrum.
Tungsten(IV) telluride (WTe2) is an inorganic semimetallic chemical compound. In October 2014, tungsten ditelluride was discovered to exhibit an extremely large magnetoresistance: 13 million percent resistance increase in a magnetic field of 60 Tesla at 0.5 Kelvin. The resistance is proportional to the square of the magnetic field and shows no saturation. This may be due to the material being the first example of a compensated semimetal, in which the number of mobile holes is the same as the number of electrons. Tungsten ditelluride has layered structure, similar to many other transition metal dichalcogenides, but its layers are so distorted that the honeycomb lattice many of them have in common is in WTe2 hard to recognize. The tungsten atoms instead form zigzag chains, which are thought to behave as one-dimensional conductors. Unlike electrons in other two dimensional semiconductors, the electrons in WTe2 can easily move between the layers.
Cuprate superconductors are a family of high-temperature superconducting materials made of layers of copper oxides (CuO2) alternating with layers of other metal oxides, which act as charge reservoirs. At ambient pressure, cuprate superconductors are the highest temperature superconductors known. However, the mechanism by which superconductivity occurs is still not understood.
Iron-based superconductors (FeSC) are iron-containing chemical compounds whose superconducting properties were discovered in 2006. In 2008, led by recently discovered iron pnictide compounds, they were in the first stages of experimentation and implementation..
Covalent superconductors are superconducting materials where the atoms are linked by covalent bonds. The first such material was boron-doped synthetic diamond grown by the high-pressure high-temperature (HPHT) method. The discovery had no practical importance, but surprised most scientists as superconductivity had not been observed in covalent semiconductors, including diamond and silicon.
The 122 iron arsenide unconventional superconductors are part of a new class of iron-based superconductors. They form in the tetragonal I4/mmm, ThCr2Si2 type, crystal structure. The shorthand name "122" comes from their stoichiometry; the 122s have the chemical formula AEFe2Pn2, where AE stands for alkaline earth metal (Ca, Ba, Sr or Eu) and Pn is pnictide (As, P, etc.). These materials become superconducting under pressure and also upon doping. The maximum superconducting transition temperature found to date is 38 K in the Ba0.6K0.4Fe2As2. The microscopic description of superconductivity in the 122s is yet unclear.
Distrontium ruthenate, also known as strontium ruthenate, is an oxide of strontium and ruthenium with the chemical formula Sr2RuO4. It was the first reported perovskite superconductor that did not contain copper. Strontium ruthenate is structurally very similar to the high-temperature cuprate superconductors, and in particular, is almost identical to the lanthanum doped superconductor (La, Sr)2CuO4. However, the transition temperature for the superconducting phase transition is 0.93 K (about 1.5 K for the best sample), which is much lower than the corresponding value for cuprates.
Iron(II) selenide refers to a number of inorganic compounds of ferrous iron and selenide (Se2−). The phase diagram of the system Fe–Se reveals the existence of several non-stoichiometric phases between ~49 at. % Se and ~53 at. % Fe, and temperatures up to ~450 °C. The low temperature stable phases are the tetragonal PbO-structure (P4/nmm) β-Fe1−xSe and α-Fe7Se8. The high temperature phase is the hexagonal, NiAs structure (P63/mmc) δ-Fe1−xSe. Iron(II) selenide occurs naturally as the NiAs-structure mineral achavalite.
CeCoIn5 ("Cerium-Cobalt-Indium 5") is a heavy-fermion superconductor with a layered crystal structure, with somewhat two-dimensional electronic transport properties. The critical temperature of 2.3 K is the highest among all of the Ce-based heavy-fermion superconductors.
Yttrium hydride is a compound of hydrogen and yttrium. It is considered to be a part of the class of rare-earth metal hydrides. It exists in several forms, the most common being a metallic compound with formula YH2. YH2 has a face-centred cubic structure, and is a metallic compound. Under great pressure, extra hydrogen can combine to yield an insulator with a hexagonal structure, with a formula close to YH3. Hexagonal YH3 has a band gap of 2.6 eV. Under pressure of 12 GPa YH3 transforms to an intermediate state, and when the pressure increases to 22 GPa another metallic face-centred cubic phase is formed.
Mikhail Ivanovich Eremets is an experimentalist in high pressure physics, chemistry and materials science. He is particularly known for his research on superconductivity, having discovered the highest critical temperature of 250 K (-23 °C) for superconductivity in lanthanum hydride under high pressures. Part of his research contains exotic manifestations of materials such as conductive hydrogen, polymeric nitrogen and transparent sodium.
A polyhydride or superhydride is a compound that contains an abnormally large amount of hydrogen. This can be described as high hydrogen stoichiometry. Examples include iron pentahydride FeH5, LiH6, and LiH7. By contrast, the more well known lithium hydride only has one hydrogen atom.
An yttrium compound is a chemical compound containing yttrium. Among these compounds, yttrium generally has a +3 valence. The solubility properties of yttrium compounds are similar to those of the lanthanides. For example oxalates and carbonates are hardly soluble in water, but soluble in excess oxalate or carbonate solutions as complexes are formed. Sulfates and double sulfates are generally soluble. They resemble the "yttrium group" of heavy lanthanide elements.
Carbonaceous sulfur hydride is a purported room-temperature superconductor that was announced in October 2020. The material is claimed to have a maximal superconducting transition temperature of 15 °C (59 °F) at a pressure of 267 gigapascals (GPa), though the validity of the claim has faced criticism. In September 2022 the article was retracted by Nature journal editorial board due to a non standard, user-defined data analysis calling into question the scientific validity of the claim.
References
- ↑ "Lanthanum decahydride". American Chemical Society.
- 1 2 3 Drozdov, A. P.; Kong, P. P.; Minkov, V. S.; Besedin, S. P.; Kuzovnikov, M. A.; Mozaffari, S.; Balicas, L.; Balakirev, F. F.; Graf, D. E.; Prakapenka, V. B.; Greenberg, E.; Knyazev, D. A.; Tkacz, M.; Eremets, M. I. (2019). "Superconductivity at 250 K in lanthanum hydride under high pressures". Nature. 569 (7757): 528–531. arXiv: 1812.01561 . Bibcode:2019Natur.569..528D. doi:10.1038/s41586-019-1201-8. PMID 31118520. S2CID 119231000.
- ↑ M. Kostrzewa; K. M. Szczęśniak; A. P. Durajski; R. Szczęśniak (31 January 2020). "From LaH10 to room–temperature superconductors". Scientific Reports. 10 (1): 1592. arXiv: 1905.12308 . Bibcode:2020NatSR..10.1592K. doi:10.1038/s41598-020-58065-9. PMC 6994605 . PMID 32005852.
- ↑ Eremets, M. I.; Minkov, V. S.; Drozdov, A. P.; Kong, P. P.; Ksenofontov, V.; Shylin, S. I.; Bud'ko, S. L.; Prozorov, R.; Balakirev, F. F.; Sun, Dan; Mozzafari, S.; Balicas, L. (10 January 2022). "High‑Temperature Superconductivity in Hydrides: Experimental Evidence and Details". Journal of Superconductivity and Novel Magnetism. 35 (4): 965–977. doi: 10.1007/s10948-022-06148-1 .
- ↑ Geballe, Zachary M.; Liu, Hanyu; Mishra, Ajay K.; Ahart, Muhtar; Somayazulu, Maddury; Meng, Yue; Baldini, Maria; Hemley, Russell J. (15 January 2018). "Synthesis and Stability of Lanthanum Superhydrides". Angewandte Chemie International Edition. 57 (3): 688–692. doi: 10.1002/anie.201709970 . PMID 29193506.
- ↑ "NNNS chemistry blog: Lanthanum decahydride". chem.vander-lingen.nl.
- ↑ Di Cataldo, Simone; Heil, Christoph; von der Linden, Wolfgang; Boeri, Lilia (2021-07-29). "BH8: Towards high-Tc low-pressure superconductivity in ternary superhydrides". Physical Review B. 104 (2): L020511. arXiv: 2102.11227 . Bibcode:2021PhRvB.104b0511D. doi:10.1103/PhysRevB.104.L020511. S2CID 242872381.