The term high-temperature superconductor was initially used to designate the new family of cuprate-perovskite ceramic materials discovered by J.G. Bednorz and K.A. Müller in 1986J. G. Bednorz and K. A. Müller, Z. Physik, B 64, 180 (1986), for which they won the Nobel prize the following year. Their discovery of the first high-temperature superconductor LBCO, with a transition temperature of 35 K, generated much excitement because it was generally believed to be impossible for superconductivity to occur at such "high" temperatures. Conventional superconductors, by contrast, require temperatures to be no higher than a few degrees above absolute zero (−273.15 °C or −459.67 °F)). High-temperature superconductors are generally considered to be those that demonstrate superconductivity at or above the temperature of liquid nitrogen, or −196 °C (77 K), since this is the most easily attainable cryogenic temperature. Though it is extremely cold by everyday standards, in the field of superconductivity, 77 K counts as high temperature.

Recently, other unconventional superconductors have been discovered. Some of them also have unusually high values of the critical temperature T_c, and hence they are sometimes also called high-temperature superconductors, although the record is still held by a cuprate perovskite material (T_c=138 K, that is −135 °C). Nevertheless it is believed by some researchers that if room temperature superconductivity is ever achieved it will be in a different family of materials.

Most prominent materials in the high-T_c range are the so-called cuprates, such as La_1.85Ba_0.15CuO₄, YBCO (Yttrium-Barium-Copper-Oxide) and related substances.

All known high-T_c 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-T_c superconductors capable of sustaining much higher magnetic fields.

One of the top unsolved problems in physics is the question of why these materials are superconductors, that is, what mechanism causes the electrons in these crystals to form pairs? Despite much intensive research and many promising leads, an answer to this question has so far eluded scientists. One reason for this is that the materials are generally complex, multi-layered crystals (for example, BSCCO), making theoretical modeling very difficult. But with the rapid rate of new, important discoveries in the field, many researchers believe the answer could come any day now.

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