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Type-1.5 Superconductor
Type-1.5 superconductors are multicomponent superconductors characterized by two or more Superconducting coherence length, coherence lengths, at least one of which is shorter than the magnetic field London penetration depth, penetration length \lambda, and at least one of which is longer. This is in contrast to single-component superconductors, where there is only one coherence length \xi and the superconductor is necessarily either type 1 (\xi > \lambda) or type 2 (\xi \sqrt \lambda and \xi \lambda>\xi_2. Additional condition of thermodynamic stability is satisfied for a range of parameters. These vortices have a nonmonotonic interaction: they attract each other at large distances and repel each other at short distances. It was shown that there is a range of parameters where these vortices are energetically favorable enough to be excitable by an external field, attractive interaction notwithstanding. This results in the formation of a special superconducting phase in low magnetic f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superconducting Coherence Length
In superconductivity, the superconducting coherence length, usually denoted as \xi (Greek lowercase ''xi''), is the characteristic exponent of the variations of the density of superconducting component. The superconducting coherence length is one of two parameters in the Ginzburg–Landau theory of superconductivity. It is given by: : \xi = \sqrt where \alpha(T) is a parameter in the Ginzburg–Landau theory#Simple interpretation, Ginzburg–Landau equation for \psi with the form \alpha_0 (T-T_c), where \alpha_0 is a constant. In Landau mean-field theory, at temperatures T near the superconducting critical temperature T_c, \xi (T) \propto (1-T/T_c)^. Up to a factor of \sqrt, it is equivalent to the characteristic exponent describing a recovery of the order parameter away from a perturbation in the theory of the second order phase transitions. In some special limiting case (mathematics), limiting cases, for example in the weak-coupling BCS theory of isotropic s-wave superconducto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Magnesium Diboride
Magnesium diboride is the inorganic compound of magnesium and boron with the formula MgB2. It is a dark gray, water-insoluble solid. The compound becomes superconducting at 39 K (−234 °C), which has attracted attention. In terms of its composition, MgB2 differs strikingly from most low-temperature superconductors, which feature mainly transition metals. Its superconducting mechanism is primarily described by BCS theory. Superconductivity Magnesium diboride's superconducting properties were discovered in 2001. Its critical temperature (''T''c) of is the highest amongst conventional superconductors. Among conventional ( phonon-mediated) superconductors, it is unusual. Its electronic structure is such that there exist two types of electrons at the Fermi level with widely differing behaviours, one of them ( sigma-bonding) being much more strongly superconducting than the other ( pi-bonding). This is at odds with usual theories of phonon-mediated superconductivity which ass ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Superconducting Coherence Length
In superconductivity, the superconducting coherence length, usually denoted as \xi (Greek lowercase ''xi''), is the characteristic exponent of the variations of the density of superconducting component. The superconducting coherence length is one of two parameters in the Ginzburg–Landau theory of superconductivity. It is given by: : \xi = \sqrt where \alpha(T) is a parameter in the Ginzburg–Landau theory#Simple interpretation, Ginzburg–Landau equation for \psi with the form \alpha_0 (T-T_c), where \alpha_0 is a constant. In Landau mean-field theory, at temperatures T near the superconducting critical temperature T_c, \xi (T) \propto (1-T/T_c)^. Up to a factor of \sqrt, it is equivalent to the characteristic exponent describing a recovery of the order parameter away from a perturbation in the theory of the second order phase transitions. In some special limiting case (mathematics), limiting cases, for example in the weak-coupling BCS theory of isotropic s-wave superconducto ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phase Transition
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic State of matter, states of matter: solid, liquid, and gas, and in rare cases, plasma (physics), plasma. A phase of a thermodynamic system and the states of matter have uniform physical property, physical properties. During a phase transition of a given medium, certain properties of the medium change as a result of the change of external conditions, such as temperature or pressure. This can be a discontinuous change; for example, a liquid may become gas upon heating to its boiling point, resulting in an abrupt change in volume. The identification of the external conditions at which a transformation occurs defines the phase transition point. Types of phase transition States of matter Phase transitions commonly refer to when a substance tran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Metallic Hydrogen
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. At high pressure and temperatures, metallic hydrogen can exist as a partial liquid rather than a solid, and researchers think it might be present in large quantities in the hot and gravitationally compressed interiors of Jupiter and Saturn, as well as in some exoplanets. Theoretical predictions Hydrogen under pressure Though often placed at the top of the alkali metal column in the periodic table, hydrogen does not, under ordinary conditions, exhibit the properties of an alkali metal. Instead, it forms diatomic molecules, similar to halogens and some nonmetals in the second period of the periodic table, such as nitrogen and oxygen. Diatomic hydrogen is a gas that, at atmospheric pressure, liquefies and solidifies only at very low temperature (20 K and 14 K respectively ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Band Structure
In solid-state physics, the electronic band structure (or simply band structure) of a solid describes the range of energy levels that electrons may have within it, as well as the ranges of energy that they may not have (called ''band gaps'' or ''forbidden bands''). Band theory derives these bands and band gaps by examining the allowed quantum mechanical wave functions for an electron in a large, periodic lattice of atoms or molecules. Band theory has been successfully used to explain many physical properties of solids, such as electrical resistivity and optical absorption, and forms the foundation of the understanding of all solid-state devices (transistors, solar cells, etc.). Why bands and band gaps occur The formation of electronic bands and band gaps can be illustrated with two complementary models for electrons in solids. The first one is the nearly free electron model, in which the electrons are assumed to move almost freely within the material. In this model, the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Oxypnictide
In chemistry, oxypnictides are a class of materials composed of oxygen, a pnictogen (group-V, especially phosphorus and arsenic) and one or more other elements. Although this group of compounds has been recognized since 1995, interest in these compounds increased dramatically after the publication of the superconducting properties of LaOFeP and LaOFeAs which were discovered in 2006 and 2008. In these experiments the oxide was partly replaced by fluoride. These and related compounds (e.g. the 122 iron arsenides) form a new group of iron-based superconductors known as iron pnictides or ferropnictides since the oxygen is not essential but the iron seems to be. Oxypnictides have been patented as magnetic semiconductors in early 2006. The different subclasses of oxypnictides are oxynitrides, oxyphosphides, oxyarsenides, oxyantimonides, and oxybismuthides. Structure Many of the oxypnictides show a layered structure. For example, LaFePO with layers of La3+O2− and Fe2+P3−. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ginzburg–Landau Theory
In physics, Ginzburg–Landau theory, often called Landau–Ginzburg theory, named after Vitaly Ginzburg and Lev Landau, is a mathematical physical theory used to describe superconductivity. In its initial form, it was postulated as a phenomenological model which could describe type-I superconductors without examining their microscopic properties. One GL-type superconductor is the famous YBCO, and generally all cuprates. Later, a version of Ginzburg–Landau theory was derived from the Bardeen–Cooper–Schrieffer microscopic theory by Lev Gor'kov, thus showing that it also appears in some limit of microscopic theory and giving microscopic interpretation of all its parameters. The theory can also be given a general geometric setting, placing it in the context of Riemannian geometry, where in many cases exact solutions can be given. This general setting then extends to quantum field theory and string theory, again owing to its solvability, and its close relation to other, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
London Penetration Depth
In superconductors, the London penetration depth (usually denoted as \lambda or \lambda_L) characterizes the distance to which a magnetic field penetrates into a superconductor and becomes equal to e^ times that of the magnetic field at the surface of the superconductor. Typical values of λL range from 50 to 500 nm. It was first derived by Geertruida de Haas-Lorentz in 1925, and later by Fritz and Heinz London in their London equations (1935).Fossheim, Kristian, and Asle Sudbø. ''Superconductivity: physics and applications''. John Wiley & Sons, 2005. The London penetration depth results from considering the London equation and Ampère's circuital law. If one considers a superconducting half-space, i.e. superconducting for x>0, and weak external magnetic field B0 applied along ''z'' direction in the empty space ''x''<0, then inside the superconductor the magnetic field is given by |
Quantum Vortex
In physics, a quantum vortex represents a quantized flux circulation of some physical quantity. In most cases, quantum vortices are a type of topological defect exhibited in superfluids and superconductors. The existence of quantum vortices was first predicted by Lars Onsager in 1949 in connection with superfluid helium. Onsager reasoned that quantisation of vorticity is a direct consequence of the existence of a superfluid order parameter as a spatially continuous wavefunction. Onsager also pointed out that quantum vortices describe the circulation of superfluid and conjectured that their excitations are responsible for superfluid phase transitions. These ideas of Onsager were further developed by Richard Feynman in 1955 and in 1957 were applied to describe the magnetic phase diagram of type-II superconductors by Alexei Alexeyevich Abrikosov. In 1935 Fritz London published a very closely related work on magnetic flux quantization in superconductors. London's fluxoid can also be ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Type-II Superconductors
In superconductivity, a type-II superconductor is a superconductor that exhibits an intermediate phase of mixed ordinary and superconducting properties at intermediate temperature and fields above the superconducting phases. It also features the formation of Abrikosov vortex, magnetic field vortices with an applied external magnetic field. This occurs above a certain critical field strength ''Hc1''. The vortex density increases with increasing field strength. At a higher critical field ''Hc2'', superconductivity is destroyed. Type-II superconductors do not exhibit a complete Meissner effect. History In 1935, J.N. Rjabinin and Lev Shubnikov experimentally discovered the type-II superconductors. In 1950, the theory of the two types of superconductors was further developed by Lev Landau and Vitaly Ginzburg in their paper on Ginzburg–Landau theory. In their argument, a type-I superconductor had positive Thermodynamic free energy, free energy of the superconductor-normal metal bounda ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
