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Heavy Fermion Superconductivity
Heavy fermion superconductors are a type of unconventional superconductor. The first heavy fermion superconductor, CeCu2Si2, was discovered by Frank Steglich in 1978. Since then over 30 heavy fermion superconductors were found (in materials based on Ce, U), with a critical temperature up to 2.3 K (in CeCoIn5). Heavy fermion materials are intermetallic compounds, containing rare earth or actinide elements. The f-electrons of these atoms hybridize with the normal conduction electrons leading to quasiparticles with an enhanced effective mass. From specific heat measurements \Delta C/C(T_) one knows that the Cooper pairs in the superconducting state are also formed by the heavy quasiparticles. In contrast to normal superconductors it cannot be described by BCS theory. Due to the large effective mass, the Fermi velocity is reduced and comparable to the inverse Debye frequency. This leads to the failing of the picture of electrons polarizing the lattice as an attractive force. Some ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Unconventional Superconductor
Unconventional superconductors are materials that display superconductivity which is not explained by the usual BCS theory or its extension, the Eliashberg theory. The pairing in unconventional superconductors may originate from some other mechanism than the electron–phonon interaction. Alternatively, a superconductor is unconventional if the superconducting order parameter transforms according to a non-trivial irreducible representation of the point group or space group of the system. Per definition, superconductors that break additional symmetries to ''U'' (1) symmetry are known as unconventional superconductors. History The superconducting properties of CeCu2Si2, a type of heavy fermion material, were reported in 1979 by Frank Steglich. For a long time it was believed that CeCu2Si2 was a singlet d-wave superconductor, but since the mid-2010s, this notion has been strongly contested. In the early eighties, many more unconventional, heavy fermion Superconductivity, supe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heavy Fermion
In materials science, 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 effecti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Frank Steglich
Frank Steglich (born 14 March 1941) is a German physicist and the founding director of the Max Planck Institute for Chemical Physics of Solids in Dresden, Germany. Education and career Steglich was born in Dresden and studied physics in the University of Münster and the University of Göttingen, where he received his PhD under Rudolf Hilsch. Steglich discovered the first heavy fermion superconductor, CeCu2Si2, while working as a research associate in Cologne, Germany in 1979. CeCu2Si2 is the first metallic system to be discovered in which the superconductivity is driven by electron-electron interactions, rather than the electron-phonon interaction that is responsible for conventional BCS superconductivity. The discovery of this material revolutionized research into superconductivity, establishing the reality of electronically mediated superconductivity and foreshadowing the discovery of a wide range of heavy electron superconductors, and the subsequent discovery of electronica ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
CeCoIn5
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. Material system CeCoIn5 is a member of a rich family of heavy-fermion compounds. CeIn3 is heavy-fermion metal with cubic crystal structure that orders antiferromagnetically below 10K. With applying external pressure, antiferromagnetism in CeIn3 is continuously suppressed, and a superconducting dome emerges in the phase diagram near the antiferromagnetic quantum critical point. CeCoIn5 has a tetragonal crystal structure, and the unit cell of CeCoIn5 can be considered as 'CeIn3 with an additional CoIn2 layer per unit cell'. Closely related to CeCoIn5 is the heavy-fermion material CeRhIn5, which has the same crystal structure and which orders antiferromagnetically below 4K, but does not become superconducting at ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UPt3
UPt3 is an inorganic binary intermetallic crystalline compound of platinum and uranium. Production It can be synthesised in the following ways: * as an intermetallic compound, by direct fusion of pure components according to stoichiometric calculations: :: \mathsf * by reduction of uranium dioxide with hydrogen in the presence of platinum: :: \mathsf Physical properties UPt3 forms crystals of hexagonal symmetry (some studies hypothesize a trigonal structure instead), space group P63/mmc, cell parameters ''a'' = 0.5766 nm and ''c'' = 0.4898 nm (''c'' should be understood as distance from planes), with a structure similar to nisnite (Ni3Sn) and MgCd3. The compound congruently melts at 1700 °C. The enthalpy of formation of the compound is -111 kJ/mol. At temperatures below 1 K it becomes superconducting Superconductivity is a set of physical properties observed in superconductors: materials where electrical resistance vanishes and magnetic fields are expelled from t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Uranium Ruthenium Silicide
Uranium ruthenium silicide (URu2Si2) is a heavy fermion alloy composed of uranium, ruthenium, and silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe .... URu2Si2 has the same '122' tetragonal crystal structure as many other compounds of present condensed matter research. URu2Si2 is a superconductor with a hastatic order (HO) phase below a temperature of 17.5 K. Below this temperature, it is magnetic, and below about 1.5 K it superconducts. However, the nature of the ordered phase below 17.5K is still under debate despite a wide variety of scenarios that have been proposed to explain this phase. References Correlated electrons Superconductivity Silicides Uranium compounds Ruthenium compounds {{Inorganic-compound-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
UPd2Al3
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. Discovery Heavy-fermion superconductivity was discovered already in the late 1970s (with CeCu2Si2 being the first example), but the number of heavy-fermion compounds known to superconduct was still very small in the early 1990s, when Christoph Geibel in the group of Frank Steglich found two closely related heavy-fermion superconductors, UNi2Al3 (Tc=1K) and UPd2Al3 (Tc=2K), which were published in 1991. At that point, the Tc=2.0K of UPd2Al3 was the highest cr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Cooper Pair
In condensed matter physics, a Cooper pair or BCS pair (Bardeen–Cooper–Schrieffer pair) is a pair of electrons (or other fermions) bound together at low temperatures in a certain manner first described in 1956 by American physicist Leon Cooper. Description Cooper showed that an arbitrarily small attraction between electrons in a metal can cause a paired state of electrons to have a lower energy than the Fermi energy, which implies that the pair is bound. In conventional superconductors, this attraction is due to the electron–phonon interaction. The Cooper pair state is responsible for superconductivity, as described in the BCS theory developed by John Bardeen, Leon Cooper, and John Schrieffer for which they shared the 1972 Nobel Prize in Physics. Although Cooper pairing is a quantum effect, the reason for the pairing can be seen from a simplified classical explanation. An electron in a metal normally behaves as a free particle. The electron is repelled from other electrons ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
BCS Theory
In physics, the Bardeen–Cooper–Schrieffer (BCS) theory (named after John Bardeen, Leon Cooper, and John Robert Schrieffer) 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. It was proposed by Bardeen, Cooper, and Schrieffer in 1957; they received the Nobel Prize in Physics for this theory in 1972. History Rapid progress in the understanding of superconductivity gained momentum in the mid-1950s. It began with the 1948 paper, "On the Problem of the Molecular Theory of Superconductivity", where Fritz London proposed that the phenomenological London equations may be consequences of the coherence of a quantum state. In 1953, Brian Pippard, motivated by penetration experiments, proposed that this would mo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Debye Frequency
In thermodynamics and solid-state physics, the Debye model is a method developed by Peter Debye in 1912 to estimate phonon contribution to the specific heat ( heat capacity) in a solid. It treats the vibrations of the atomic lattice (heat) as phonons in a box in contrast to the Einstein photoelectron model, which treats the solid as many individual, non-interacting quantum harmonic oscillators. The Debye model correctly predicts the low-temperature dependence of the heat capacity of solids, which is proportional to the cube of temperature – the Debye ''T'' 3 law. Similarly to the Einstein photoelectron model, it recovers the Dulong–Petit law at high temperatures. Due to simplifying assumptions, its accuracy suffers at intermediate temperatures. Derivation The Debye model treats atomic vibrations as phonons confined in the solid's volume. It is analogous to Planck's law of black body radiation, which treats electromagnetic radiation as a photon gas confined in a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superconductivity
Superconductivity is a set of physical properties observed in superconductors: materials where Electrical resistance and conductance, electrical resistance vanishes and Magnetic field, magnetic fields are expelled from the material. Unlike an ordinary metallic Electrical conductor, conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic Phase transition, 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. The superconductivity phenomenon was discovered in 1911 by Dutch physicist Heike Kamerlingh Onnes. Like ferromagnetism and Atomic spectral line, atomic spectral lines, superconductivity is a phenomenon which can only be explained by quantum mechanics. It is characterized by the Meissner effect, the complete cancellation of the magnetic field in the interior of the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
