Despite its name, high-temperature superconductivity still occurs at cryogenics temperatures. The main difference from ''low-temperature superconductivity'' is usually that 'high-Tc' superconductors can use liquid nitrogen (at 1 E1 K) as a coolant while ''low-temperature superconductors'' always need liquid helium (1 E0 K) temperatures and below. Most prominent materials in the high-Tc range are the so-called cuprates, i.e. YBCO (Yttrium-Barium-Copper-oxygen) and related substances. All known high-Tc superconductors are so-called Type-II superconductors. A Type-II superconductor allows magnetic field to penerate its interior in the units of flux quanta, creating 'holes' (or tubes) of normal metallic regions in the superconducting bulk. This property makes high-Tc superconductors capable of sustaining much higher magnetic fields. ==See also== High-temperature superconductor Superconductivity
It is not true that "low temperature superconductors" always needs liquid helium temperatures. Generically, "low temperature superconductors" are defined by not being "high temperature superconductors". This just means that they are described by the conventional BCS theory. For instance, magnesium diboride (MgB2) is the most recently discovered conventional superconductor, and it has a Tc of 35K. The BCS theory describes "phonon mediated" electron pairing. Although it cannot predict Tc, there are general arguments that say that Tc can not get above 30-35K. Some contemporary hi-Tc theories try to invoke phonons, but there is no consensus on their applicability. The largest peice of evidence against phonons is the lack of "isotope effect", where Tc is proportional to the square root of the mass of the isotopic substitution element. The extended BCS theory, which generalizes weak coupling phonons to stronger coupling, known as the Eliashberg theory, predicts that the exponent will not be exactly 1/2, but will be material dependent. ----- This page should be merged with High-temperature superconductors User:220.244.224.10 00:36, 16 Mar 2005 (UTC)
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High-temperature superconductivity
Despite its name, high-temperature superconductivity still occurs at cryogenics temperatures. The main difference from ''low-temperature superconductivity'' is usually that 'high-Tc' superconductors can use liquid nitrogen (at 1 E1 K) as a coolant while ''low-temperature superconductors'' always need liquid helium (1 E0 K) temperatures and below. Most prominent materials in the high-Tc range are the so-called cuprates, i.e. YBCO (Yttrium-Barium-Copper-oxygen) and related substances. All known high-Tc superconductors are so-called Type-II superconductors. A Type-II superconductor allows magnetic field to penerate its interior in the units of flux quanta, creating 'holes' (or tubes) of normal metallic regions in the superconducting bulk. This property makes high-Tc superconductors capable of sustaining much higher magnetic fields. ==See also== High-temperature superconductor Superconductivity
High-temperature superconductivity
It is not true that "low temperature superconductors" always needs liquid helium temperatures. Generically, "low temperature superconductors" are defined by not being "high temperature superconductors". This just means that they are described by the conventional BCS theory. For instance, magnesium diboride (MgB2) is the most recently discovered conventional superconductor, and it has a Tc of 35K. The BCS theory describes "phonon mediated" electron pairing. Although it cannot predict Tc, there are general arguments that say that Tc can not get above 30-35K. Some contemporary hi-Tc theories try to invoke phonons, but there is no consensus on their applicability. The largest peice of evidence against phonons is the lack of "isotope effect", where Tc is proportional to the square root of the mass of the isotopic substitution element. The extended BCS theory, which generalizes weak coupling phonons to stronger coupling, known as the Eliashberg theory, predicts that the exponent will not be exactly 1/2, but will be material dependent. ----- This page should be merged with High-temperature superconductors User:220.244.224.10 00:36, 16 Mar 2005 (UTC)
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