Meissner effect. Diagram of the Meissner effect.
Magnetic field lines, represented as arrows, are excluded from a superconductor when it is below its critical temperature. The Meissner effect is an expulsion of a magnetic field from a superconductor during its transition to the superconducting state. The German physicists Walther Meissner and Robert Ochsenfeld discovered the phenomenon in 1933 by measuring the magnetic field distribution outside superconducting tin and lead samples.[1] The samples, in the presence of an applied magnetic field, were cooled below their superconducting transition temperature. Below the transition temperature the samples cancelled nearly all interior magnetic fields.
They detected this effect only indirectly because the magnetic flux is conserved by a superconductor: when the interior field decreases, the exterior field increases. Explanation[edit] In a weak applied field, a superconductor "expels" nearly all magnetic flux. Perfect diamagnetism[edit] = −1. Room-temperature superconductor. A room-temperature superconductor is a hypothetical material that exhibits superconductivity at operating temperatures above 0° C (273.15 K) which, though not "room temperature" (approx. 20–25 °C) is the temperature at which ice forms and can be reached and easily maintained in an everyday environment.
The highest temperature known superconducting materials are the cuprates, which have demonstrated superconductivity at atmospheric pressure at temperatures as high as -135 °C (138 K).[1] Although research into room-temperature superconductivity[2][3] may produce no result, superconductivity has repeatedly been discovered at temperatures that were previously unexpected or held to be impossible. Reports[edit] Since the discovery of high-temperature superconductors, several materials have been reported to be room-temperature superconductors, although none of these reports has been confirmed. Theories[edit] In 1964, William A. References[edit] Jump up ^ P. High-temperature superconductivity. A small sample of the high-temperature superconductor BSCCO-2223.
High-temperature superconductors (abbreviated high-Tc or HTS) are materials that behave as superconductors at unusually[1] high temperatures. The first high-Tc superconductor was discovered in 1986 by IBM researchers Georg Bednorz and K. Alex Müller,[2][3] who were awarded the 1987 Nobel Prize in Physics "for their important break-through in the discovery of superconductivity in ceramic materials".[4] For an explanation about Tc (the critical temperature for superconductivity), see Superconductivity#Superconducting phase transition and the second bullet item of BCS theory#Successes of the BCS theory. History[edit] The phenomenon of superconductivity was discovered by Kamerlingh Onnes in 1911, in metallic mercury below 4 K (−269.15 °C). Shortly after, P. Crystal structures of high-temperature ceramic superconductors[edit] YBaCuO superconductors[edit] YBCO unit cell Bi-, Tl- and Hg-based high-Tc superconductors[edit]
Superconductivity. Video of a Meissner effect in a high temperature superconductor (black pellet) with a NdFeB magnet (metallic) A high-temperature superconductor levitating above a magnet Superconductivity is a phenomenon of exactly zero electrical resistance and expulsion of magnetic fields occurring in certain materials when cooled below a characteristic critical temperature.
It was discovered by Dutch physicist Heike Kamerlingh Onnes on April 8, 1911 in Leiden. Like ferromagnetism and atomic spectral lines, superconductivity is a quantum mechanical phenomenon. It is characterized by the Meissner effect, the complete ejection of magnetic field lines from the interior of the superconductor as it transitions into the superconducting state. Explanation[edit] The electrical resistivity of a metallic conductor decreases gradually as temperature is lowered and at the same time its conductivity becomes infinite. Classification[edit] There are many criteria by which superconductors are classified.