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BCS theory or Bardeen–Cooper–Schrieffer theory is the first microscopic theory of superconductivity since Heike Kamerlingh Onnes's 1911 discovery. The theory describes superconductivity as a microscopic effect caused by a condensation of Cooper pairs. The theory is also used in nuclear physics to describe the pairing interaction between nucleons in an atomic nucleus.
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.
In condensed matter physics, a Cooper pair or BCS pair is a pair of electrons bound together at low temperatures in a certain manner first described in 1956 by American physicist Leon Cooper.
In solid-state physics, heavy fermion materials are a specific type of intermetallic compound, containing elements with 4f or 5f electrons in unfilled electron bands. Electrons are one type of fermion, and when they are found in such materials, they are sometimes referred to as heavy electrons. Heavy fermion materials have a low-temperature specific heat whose linear term is up to 1000 times larger than the value expected from the free electron model. The properties of the heavy fermion compounds often derive from the partly filled f-orbitals of rare-earth or actinide ions, which behave like localized magnetic moments. The name "heavy fermion" comes from the fact that the fermion behaves as if it has an effective mass greater than its rest mass. In the case of electrons, below a characteristic temperature (typically 10 K), the conduction electrons in these metallic compounds behave as if they had an effective mass up to 1000 times the free particle mass. This large effective mass is also reflected in a large contribution to the resistivity from electron-electron scattering via the Kadowaki–Woods ratio. Heavy fermion behavior has been found in a broad variety of states including metallic, superconducting, insulating and magnetic states. Characteristic examples are CeCu6, CeAl3, CeCu2Si2, YbAl3, UBe13 and UPt3.
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.
Piers Coleman is a British-born theoretical physicist, working in the field of theoretical condensed matter physics. Coleman is Professor of Physics at Rutgers University in New Jersey and at Royal Holloway, University of London.
Heavy fermion superconductors are a type of unconventional superconductor.
The Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase can arise in a superconductor in large magnetic field. Among its characteristics are Cooper pairs with nonzero total momentum and a spatially non-uniform order parameter, leading to normal conducting areas in the superconductor.
Girsh Blumberg is an Estonian-American experimental physicist working in the field of experimental condensed matter physics, spectroscopy, nano-optics, and plasmonics. Blumberg is an elected fellow of the American Physical Society , an elected fellow of the American Association for the Advancement of Science (FAAAS) , and a Distinguished Professor of Physics at Rutgers University.
The EPS CMD Europhysics Prize is awarded since 1975 by the Condensed Matter Division of the European Physical Society, in recognition of recent work by one or more individuals, for scientific excellence in the area of condensed matter physics. It is one of Europe’s most prestigious prizes in the field of condensed matter physics. Several laureates of the EPS CMD Europhysics Prize also received a Nobel Prize in Physics or Chemistry.
Peter Fulde is a physicist working in condensed matter theory and quantum chemistry.
Laura H. Greene is the Marie Krafft Professor of Physics at Florida State University and Chief Scientist at the National High Magnetic Field Laboratory. She was previously a professor of physics at the University of Illinois at Urbana-Champaign. In September 2021, she was appointed to the President's Council of Advisors on Science and Technology (PCAST).
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.
Elihu Abrahams was a theoretical physicist, specializing in condensed matter physics.
UPd2Al3 is a heavy-fermion superconductor with a hexagonal crystal structure and critical temperature Tc=2.0K that was discovered in 1991. Furthermore, UPd2Al3 orders antiferromagnetically at TN=14K, and UPd2Al3 thus features the unusual behavior that this material, at temperatures below 2K, is simultaneously superconducting and magnetically ordered. Later experiments demonstrated that superconductivity in UPd2Al3 is magnetically mediated, and UPd2Al3 therefore serves as a prime example for non-phonon-mediated superconductors.
Gilbert "Gil" George Lonzarich is a solid-state physicist who works at the Cavendish Laboratory at the University of Cambridge. He is particularly noted for his work on superconducting and magnetic materials.
Boris Ivanovich Kochelaev is a Soviet and Russian physicist and professor.
Yurii Georgiyovych Naidyuk is a Ukrainian physicist, Director of the B.I. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine. He is a corresponding member of the National Academy of Sciences of Ukraine (NASU). He has been awarded the State Prize of Ukraine in Science and Technology and the B. I. Verkin Prize of the National Academy of Sciences of Ukraine. He is the editor-in-chief of the academic journal Low Temperature Physics.
References
- ↑ F. Steglich (2005). "Twenty-five years of heavy-fermion superconductivity". Physica B: Condensed Matter. 359–361: 326–332. Bibcode:2005PhyB..359..326S. doi:10.1016/j.physb.2005.01.054.
- ↑ F. Steglich; J. Aarts; C. D. Bredl; W. Lieke; D. Meschede; W. Franz; H. Schäfer (1979). "Superconductivity in the Presence of Strong Pauli Paramagnetism: CeCu2Si2". Physical Review Letters . 43 (25): 1892. Bibcode:1979PhRvL..43.1892S. doi:10.1103/PhysRevLett.43.1892. hdl: 1887/81461 .
