“superconductivity”的概念、定义、翻译、参考文献-科学参考

superconductivity

Physics

The absence of measurable electrical resistance in certain substances at temperatures close to 0 K. First discovered in mercury (1911) by Heike Kamerling Onnes (1853–1926), superconductivity is now known to occur in some 26 metallic elements and many compounds and alloys. The temperature below which a substance becomes superconducting is called the transition temperature (or critical temperature). Compounds are now known that show superconductivity at liquid-nitrogen temperatures.

The theoretical explanation of the phenomenon was given by John Bardeen, Leon Cooper (1930– ), and Robert Schrieffer (1931–2019) in 1957 and is known as the BCS theory. According to this theory an electron moving through an elastic crystal lattice creates a slight distortion of the lattice as a result of Coulomb forces between the positively charged lattice and the negatively charged electron. If this distortion persists for a finite time it can affect a second passing electron. In 1956 Cooper showed that the effect of this phenomenon is for the current to be carried in superconductors not by individual electrons but by bound pairs of electrons, the Cooper pairs. The BCS theory is based on a wave function in which all the electrons are paired. Because the total momentum of a Cooper pair is unchanged by the interaction between one of its electrons and the lattice, the flow of electrons continues indefinitely.

Superconducting coils in which large currents can circulate indefinitely can be used to create powerful magnetic fields and are used for this purpose in some particle accelerators and in other devices.

Superconductivity can also occur by a slightly more complicated mechanism than BCS theory in heavy-fermion systems. In 1986, Georg Bednorz (1950– ) and Karl Müller (1927– ) found an apparently completely different type of superconductivity. This is called high-temperature superconductivity, since the critical temperature is very much higher than for BCS superconductors; some high-temperature superconductors have critical temperatures greater than 100 K. A typical high-temperature superconductor is YBa₂Cu₃O₁₋₇.

At the present time a theory of high-temperature superconductivity has not been established in spite of a great deal of effort, which is still going on. The BCS mechanism, and minor modifications of it, almost certainly do not apply. Some models of high-temperature superconductors have had some successes in explaining some of the properties of these materials, but a unified theory has not yet been produced.

http://www.kayelaby.npl.co.uk/general_physics/2_6/2_6_4.html Properties of superconducting elements at the NPL website

Chemistry

The property possessed by some substances below a certain temperature, the transition point, of zero resistance. Until recently, the known superconducting materials had very low transition points. However, synthetic organic conductors and certain metal oxide ceramics have now been produced that become superconducting at much higher temperatures. For example, much work has been done on ytterbium-barium-copper oxides, which have transition temperatures of about 100 K.

Computer

The physical phenomenon that causes some materials to have zero electrical resistance when held at very low temperatures. Superconductivity is of interest to computer engineers since it points to the possibility of great computing power with little or no heat generation. This is especially so since the recent demonstration of superconductivity in certain complex metallic oxides at relatively high temperatures.

Electronics and Electrical Engineering

A phenomenon that occurs in certain metals and a large number of compounds and alloys when cooled to a temperature close to the absolute zero of thermodynamic temperature. At temperatures below a critical transition temperature, T_c, the electrical resistance of the material becomes vanishingly small and the material behaves as a perfect conductor. Currents induced in superconducting material have persisted for several years without significant decay.
The material also exhibits perfect diamagnetism in weak magnetic fields: the magnetic flux density inside the material is zero. If the material is in the form of a hollow cylinder, the magnetic flux density contained in the hollow region remains constant and trapped in the state existing at the transition temperature, while the flux density within the material becomes zero. These magnetic effects are termed Meissner effects. If the value of applied magnetic flux density rises to a value greater than a critical value, B_c, the superconductivity is destroyed. The value of B_c – the transition flux density – is a function of the temperature of the material and its nature. A superconducting current in the material itself can produce an associated magnetic flux density greater than the critical value; there is therefore an upper limit to the current density that may be sustained by the material in the superconducting state. Certain alloys have relatively high transition temperatures and high critical field values and are used in superconducting magnets. Niobium-tin (Nb₃Sn) for example can produce a magnetic field of about 12 tesla at 4.2 kelvin, i.e. at the boiling point of liquid helium. Other transition metal compounds such as Nb₃Ge have transition temperatures at around the boiling point of liquid hydrogen (20 K). Such compounds fall into the Al5 series, i.e. they have a crystallographic structure similar to beta-tungsten.
High-temperature superconductivity with transition temperatures of 90 K or above has been demonstrated using complex ceramic oxides that contain rare earth elements or transition metals and have the general composition
${RBa}_{2} {Cu}_{3} O_{1 - 7}$
where R is a rare earth ion or transition metal. Scandium, lanthanum, neodymium, ytterbium, and several other elements have all been successfully used to obtain samples of high-temperature superconductors (HTS).
Implementation of devices and systems using high-temperature superconductors has proved difficult because of the magnetic flux density produced when large electric currents flow in the HTS. Although a strong magnetic field destroys the superconductivity and a weak field cannot penetrate the material, at intermediate field strengths the field penetrates the HTS in thin tubes running across the material. In the core of each tube is a ‘tornado’ of electric current, and the tubes are thus known as vortices. Outside each vortex the material remains superconducting but within each vortex the superconductivity is destroyed. As the magnetic field-strength increases so do the number and density of the vortices. The current applied to the superconductor causes the vortices to move, which dissipates electrical energy, producing resistance. Vortices act like atoms and can form into solid or liquid states of vortex matter depending on the temperature and magnetic field strength. Locking vortices in place, for example by introducing crystal defects to trap them or by twisting vortices around one another, leads to HTS with better electrical properties.
One of the most successful theories of superconductivity at the lowest temperatures was given in 1957 by Bardeen, Cooper, and Schrieffer. This is the BCS theory in which electron pairs – Cooper pairs – can form in the presence of other electrons. The pairing results from interactions between the electrons and the quantized vibrations of the crystal lattice – phonons – and produces a highly ordered state with no dissipation of energy in the electron movement. The BCS theory, however, proposes a singlet pair state. At higher temperatures this is not sufficient to fully explain the phenomenon and various ideas have been proposed to explain the postulated attractive interactions between electrons and the configuration of the electron pairs. An understanding of the theoretical basis for superconductivity will be determined by careful analysis of data from experiments carried out on single crystal samples, and should help the search for materials with even higher critical temperatures.
The Josephson effect occurs when an extremely thin layer of insulating material is introduced into a superconductor. A current, below a certain critical value, can flow across the insulator in the absence of an applied voltage.
http://www.supraconductivite.fr/en/index.php Introduction to superconductivity, from the CNRS and two other French research organizations

单词	superconductivity
释义	superconductivity Physics The absence of measurable electrical resistance in certain substances at temperatures close to 0 K. First discovered in mercury (1911) by Heike Kamerling Onnes (1853–1926), superconductivity is now known to occur in some 26 metallic elements and many compounds and alloys. The temperature below which a substance becomes superconducting is called the transition temperature (or critical temperature). Compounds are now known that show superconductivity at liquid-nitrogen temperatures. The theoretical explanation of the phenomenon was given by John Bardeen, Leon Cooper (1930– ), and Robert Schrieffer (1931–2019) in 1957 and is known as the BCS theory. According to this theory an electron moving through an elastic crystal lattice creates a slight distortion of the lattice as a result of Coulomb forces between the positively charged lattice and the negatively charged electron. If this distortion persists for a finite time it can affect a second passing electron. In 1956 Cooper showed that the effect of this phenomenon is for the current to be carried in superconductors not by individual electrons but by bound pairs of electrons, the Cooper pairs. The BCS theory is based on a wave function in which all the electrons are paired. Because the total momentum of a Cooper pair is unchanged by the interaction between one of its electrons and the lattice, the flow of electrons continues indefinitely. Superconducting coils in which large currents can circulate indefinitely can be used to create powerful magnetic fields and are used for this purpose in some particle accelerators and in other devices. Superconductivity can also occur by a slightly more complicated mechanism than BCS theory in heavy-fermion systems. In 1986, Georg Bednorz (1950– ) and Karl Müller (1927– ) found an apparently completely different type of superconductivity. This is called high-temperature superconductivity, since the critical temperature is very much higher than for BCS superconductors; some high-temperature superconductors have critical temperatures greater than 100 K. A typical high-temperature superconductor is YBa₂Cu₃O₁₋₇. At the present time a theory of high-temperature superconductivity has not been established in spite of a great deal of effort, which is still going on. The BCS mechanism, and minor modifications of it, almost certainly do not apply. Some models of high-temperature superconductors have had some successes in explaining some of the properties of these materials, but a unified theory has not yet been produced. http://www.kayelaby.npl.co.uk/general_physics/2_6/2_6_4.html Properties of superconducting elements at the NPL website Chemistry The property possessed by some substances below a certain temperature, the transition point, of zero resistance. Until recently, the known superconducting materials had very low transition points. However, synthetic organic conductors and certain metal oxide ceramics have now been produced that become superconducting at much higher temperatures. For example, much work has been done on ytterbium-barium-copper oxides, which have transition temperatures of about 100 K. Computer The physical phenomenon that causes some materials to have zero electrical resistance when held at very low temperatures. Superconductivity is of interest to computer engineers since it points to the possibility of great computing power with little or no heat generation. This is especially so since the recent demonstration of superconductivity in certain complex metallic oxides at relatively high temperatures. Electronics and Electrical Engineering A phenomenon that occurs in certain metals and a large number of compounds and alloys when cooled to a temperature close to the absolute zero of thermodynamic temperature. At temperatures below a critical transition temperature, T_c, the electrical resistance of the material becomes vanishingly small and the material behaves as a perfect conductor. Currents induced in superconducting material have persisted for several years without significant decay. The material also exhibits perfect diamagnetism in weak magnetic fields: the magnetic flux density inside the material is zero. If the material is in the form of a hollow cylinder, the magnetic flux density contained in the hollow region remains constant and trapped in the state existing at the transition temperature, while the flux density within the material becomes zero. These magnetic effects are termed Meissner effects. If the value of applied magnetic flux density rises to a value greater than a critical value, B_c, the superconductivity is destroyed. The value of B_c – the transition flux density – is a function of the temperature of the material and its nature. A superconducting current in the material itself can produce an associated magnetic flux density greater than the critical value; there is therefore an upper limit to the current density that may be sustained by the material in the superconducting state. Certain alloys have relatively high transition temperatures and high critical field values and are used in superconducting magnets. Niobium-tin (Nb₃Sn) for example can produce a magnetic field of about 12 tesla at 4.2 kelvin, i.e. at the boiling point of liquid helium. Other transition metal compounds such as Nb₃Ge have transition temperatures at around the boiling point of liquid hydrogen (20 K). Such compounds fall into the Al5 series, i.e. they have a crystallographic structure similar to beta-tungsten. High-temperature superconductivity with transition temperatures of 90 K or above has been demonstrated using complex ceramic oxides that contain rare earth elements or transition metals and have the general composition ${RBa}_{2} {Cu}_{3} O_{1 - 7}$ where R is a rare earth ion or transition metal. Scandium, lanthanum, neodymium, ytterbium, and several other elements have all been successfully used to obtain samples of high-temperature superconductors (HTS). Implementation of devices and systems using high-temperature superconductors has proved difficult because of the magnetic flux density produced when large electric currents flow in the HTS. Although a strong magnetic field destroys the superconductivity and a weak field cannot penetrate the material, at intermediate field strengths the field penetrates the HTS in thin tubes running across the material. In the core of each tube is a ‘tornado’ of electric current, and the tubes are thus known as vortices. Outside each vortex the material remains superconducting but within each vortex the superconductivity is destroyed. As the magnetic field-strength increases so do the number and density of the vortices. The current applied to the superconductor causes the vortices to move, which dissipates electrical energy, producing resistance. Vortices act like atoms and can form into solid or liquid states of vortex matter depending on the temperature and magnetic field strength. Locking vortices in place, for example by introducing crystal defects to trap them or by twisting vortices around one another, leads to HTS with better electrical properties. One of the most successful theories of superconductivity at the lowest temperatures was given in 1957 by Bardeen, Cooper, and Schrieffer. This is the BCS theory in which electron pairs – Cooper pairs – can form in the presence of other electrons. The pairing results from interactions between the electrons and the quantized vibrations of the crystal lattice – phonons – and produces a highly ordered state with no dissipation of energy in the electron movement. The BCS theory, however, proposes a singlet pair state. At higher temperatures this is not sufficient to fully explain the phenomenon and various ideas have been proposed to explain the postulated attractive interactions between electrons and the configuration of the electron pairs. An understanding of the theoretical basis for superconductivity will be determined by careful analysis of data from experiments carried out on single crystal samples, and should help the search for materials with even higher critical temperatures. The Josephson effect occurs when an extremely thin layer of insulating material is introduced into a superconductor. A current, below a certain critical value, can flow across the insulator in the absence of an applied voltage. http://www.supraconductivite.fr/en/index.php Introduction to superconductivity, from the CNRS and two other French research organizations
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