Superconductor
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** WHAT IS THE SECRET OF SO CALLED “ZERO RESISTANCE /RESISTIVITY”OR EXPALIN THE HYPOTHETICAL CONCEPTS ON ROOM TEMPERATURE SUPER CONDUCTIVITY..?
Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently-discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared. In subsequent decades, superconductivity was found in several other materials. In 1913, lead was found to super conduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. The next important step in understanding superconductivity occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect. In 1935, F. and H. London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current. The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper, and Schrieffer. Independently, the superconductivity phenomenon was explained by Nikolay Bogolyubov. This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. Superconductivity is a phenomenon occurring in certain materials at extremely low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field (the Meissner effect). The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, impurities and other defects impose a lower limit. Even near absolute zero a real sample of copper shows a non-zero resistance. The resistance of a superconductor, on the other hand, drops abruptly to zero when the material is cooled below its "critical temperature". An electrical current flowing in a loop of superconducting wire can persist indefinitely with no power source. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It cannot be understood simply as the idealization of "perfect conductivity" in classical physics. Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys and some heavily-doped semiconductors. Superconductivity does not occur in noble metals like gold and silver, nor in most ferromagnetic metals. A room-temperature superconductor is a material yet to be discovered which would be capable of exhibiting superconducting properties at temperatures above 0° C (273.15 K). This is of course not strictly speaking "room temperature" (20–25° C), however it can be reached very cheaply.
Since the discovery of high-temperature superconductors,( High-temperature superconductors (abbreviated high Tc) are a family of superconducting materials containing copper-oxide planes as a common structural feature. For this reason, the term is often used interchangeably with cuprate superconductors. This feature allows some materials to support superconductivity at temperatures above the boiling point of liquid nitrogen (77 K or -196°C). Indeed, they offer the highest transition temperatures of all superconductors. The ability to use relatively inexpensive and easily handled liquid nitrogen as a coolant has increased the range of practical applications of superconductivity.) Several materials have been claimed as being room-temperature superconductors. In every case, independent investigation has quickly proven these claims false. As a result, most condensed matter physicists now welcome with extreme skepticism any further claims of this nature. As of 2006, the highest-temperature superconductor (at ambient pressure) is mercury thallium barium calcium copper oxide (Hg12Tl3Ba30Ca30Cu45O125), at 138 K, though there are claims that this can be raised to 164 K by applying high pressure to the superconductor. More information on this subject can be found here: http://xxx.lanl.gov/ftp/condmat/papers/0606/0606187.pdf . A potential candidate for room temperature superconductivity is metallic hydrogen. Theory has been put forward by N.W. Ashcroft that metallic hydrogen may be a superconductor as high as room temperature (290K), far higher than any other known candidate material. This stems from its extremely high speed of sound and the expected strong coupling between the conduction electrons and the lattice vibrations.[6] 1. GIVE THE POSSIBLE ARGUMENTS ON THERMAL AND ELECTRICAL RELAXATION TIMES (USE WIEDEMANN –FRANZ LAW)..?
Superconductivity was discovered in 1911 by Heike Kamerlingh Onnes, who was studying the resistance of solid mercury at cryogenic temperatures using the recently-discovered liquid helium as a refrigerant. At the temperature of 4.2 K, he observed that the resistance abruptly disappeared. In subsequent decades, superconductivity was found in several other materials. In 1913, lead was found to super conduct at 7 K, and in 1941 niobium nitride was found to superconduct at 16 K. The next important step in understanding superconductivity occurred in 1933, when Meissner and Ochsenfeld discovered that superconductors expelled applied magnetic fields, a phenomenon which has come to be known as the Meissner effect. In 1935, F. and H. London showed that the Meissner effect was a consequence of the minimization of the electromagnetic free energy carried by superconducting current. The complete microscopic theory of superconductivity was finally proposed in 1957 by Bardeen, Cooper, and Schrieffer. Independently, the superconductivity phenomenon was explained by Nikolay Bogolyubov. This BCS theory explained the superconducting current as a superfluid of Cooper pairs, pairs of electrons interacting through the exchange of phonons. For this work, the authors were awarded the Nobel Prize in 1972. Superconductivity is a phenomenon occurring in certain materials at extremely low temperatures, characterized by exactly zero electrical resistance and the exclusion of the interior magnetic field (the Meissner effect). The electrical resistivity of a metallic conductor decreases gradually as the temperature is lowered. However, in ordinary conductors such as copper and silver, impurities and other defects impose a lower limit. Even near absolute zero a real sample of copper shows a non-zero resistance. The resistance of a superconductor, on the other hand, drops abruptly to zero when the material is cooled below its "critical temperature". An electrical current flowing in a loop of superconducting wire can persist indefinitely with no power source. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It cannot be understood simply as the idealization of "perfect conductivity" in classical physics. Superconductivity occurs in a wide variety of materials, including simple elements like tin and aluminium, various metallic alloys and some heavily-doped semiconductors. Superconductivity does not occur in noble metals like gold and silver, nor in most ferromagnetic metals. A room-temperature superconductor is a material yet to be discovered which would be capable of exhibiting superconducting properties at temperatures above 0° C (273.15 K). This is of course not strictly speaking "room temperature" (20–25° C), however it can be reached very cheaply.
Since the discovery of high-temperature superconductors,( High-temperature superconductors (abbreviated high Tc) are a family of superconducting materials containing copper-oxide planes as a common structural feature. For this reason, the term is often used interchangeably with cuprate superconductors. This feature allows some materials to support superconductivity at temperatures above the boiling point of liquid nitrogen (77 K or -196°C). Indeed, they offer the highest transition temperatures of all superconductors. The ability to use relatively inexpensive and easily handled liquid nitrogen as a coolant has increased the range of practical applications of superconductivity.) Several materials have been claimed as being room-temperature superconductors. In every case, independent investigation has quickly proven these claims false. As a result, most condensed matter physicists now welcome with extreme skepticism any further claims of this nature. As of 2006, the highest-temperature superconductor (at ambient pressure) is mercury thallium barium calcium copper oxide (Hg12Tl3Ba30Ca30Cu45O125), at 138 K, though there are claims that this can be raised to 164 K by applying high pressure to the superconductor. More information on this subject can be found here: http://xxx.lanl.gov/ftp/condmat/papers/0606/0606187.pdf . A potential candidate for room temperature superconductivity is metallic hydrogen. Theory has been put forward by N.W. Ashcroft that metallic hydrogen may be a superconductor as high as room temperature (290K), far higher than any other known candidate material. This stems from its extremely high speed of sound and the expected strong coupling between the conduction electrons and the lattice vibrations.[6] 1. GIVE THE POSSIBLE ARGUMENTS ON THERMAL AND ELECTRICAL RELAXATION TIMES (USE WIEDEMANN –FRANZ LAW)..?
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