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High-temperature superconductors (abbreviated high-''T''c or HTS) are materials that behave as superconductors at unusually high temperatures. The first high-''T''c superconductor was discovered in 1986 by IBM researchers Georg Bednorz and K. Alex Müller,〔 〕 who were awarded the 1987 Nobel Prize in Physics "for their important break-through in the discovery of superconductivity in ceramic materials".〔(The Nobel Prize in Physics 1987: J. Georg Bednorz, K. Alex Müller ). Nobelprize.org. Retrieved 2012-04-19.〕 Whereas "ordinary" or metallic superconductors usually have transition temperatures (temperatures below which they superconduct) below , and must be cooled using liquid helium in order to achieve superconductivity, HTS have been observed with transition temperatures as high as , and can be cooled to superconductivity using liquid nitrogen.〔 Until 2008, only certain compounds of copper and oxygen (so-called "cuprates") were believed to have HTS properties, and the term high-temperature superconductor was used interchangeably with cuprate superconductor for compounds such as bismuth strontium calcium copper oxide (BSCCO) and yttrium barium copper oxide (YBCO). Several iron-based compounds (the iron pnictides) are now known to be superconducting at high temperatures.〔〔Choi, Charles Q. (Iron Exposed as High-Temperature Superconductor: Scientific American ). April 23, 2008. Retrieved 2012-04-19.〕〔 〕 For an explanation about ''T''c (the critical temperature for superconductivity), see and the second bullet item of . ==History== The phenomenon of superconductivity was discovered by Kamerlingh Onnes in 1911, in metallic mercury below . For seventy-five years after that, researchers attempted to observe superconductivity at higher and higher temperatures. In the late 1970s, superconductivity was observed in certain metal oxides at temperatures as high as , which were much higher than those for elemental metals. In 1986, J. Georg Bednorz and K. Alex Müller, working at the IBM research lab near Zurich, Switzerland were exploring a new class of ceramics for superconductivity. Bednorz encountered a barium-doped compound of lanthanum and copper oxide whose resistance dropped down to zero at a temperature around .〔 Their results were soon confirmed〔Stuart A Wolf & Vladimir Z Kresin,Eds, Novel Superconductivity, Springer (October, 1987)〕 by many groups, notably Paul Chu at the University of Houston and Shoji Tanaka at the University of Tokyo. Shortly after, P. W. Anderson, at Princeton University came up with the first theoretical description of these materials, using the resonating valence bond theory, but a full understanding of these materials is still developing today. These superconductors are now known to possess a d-wave pair symmetry. The first proposal that high-temperature cuprate superconductivity involves d-wave pairing was made in 1987 by Bickers, Scalapino and Scalettar, followed by three subsequent theories in 1988 by Inui, Doniach, Hirschfeld and Ruckenstein, using spin-fluctuation theory, and by Gros, Poilblanc, Rice and Zhang, and by Kotliar and Liu identifying d-wave pairing as a natural consequence of the RVB theory. The confirmation of the d-wave nature of the cuprate superconductors was made by a variety of experiments, including the direct observation of the d-wave nodes in the excitation spectrum through Angle Resolved Photoemission Spectroscopy, the observation of a half-integer flux in tunneling experiments, and indirectly from the temperature dependence of the penetration depth, specific heat and thermal conductivity. The superconductor with the highest transition temperature that has been confirmed by multiple independent research groups (a prerequisite to be called a discovery, verified by peer review) is mercury barium calcium copper oxide (HgBa2Ca2Cu3O8) at around 133 K. After more than twenty years of intensive research, the origin of high-temperature superconductivity is still not clear, but it seems that instead of ''electron-phonon'' attraction mechanisms, as in conventional superconductivity, one is dealing with genuine ''electronic'' mechanisms (e.g. by antiferromagnetic correlations), and instead of s-wave pairing, d-waves are substantial. One goal of all this research is room-temperature superconductivity. In 2014, evidence showing that fractional particles can happen in quasi two-dimensional magnetic materials, was found by EPFL scientists lending support for Anderson's theory of high-temperature superconductivity. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「High-temperature superconductivity」の詳細全文を読む スポンサード リンク
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