Unconventional Superconductor - History and Progress

History and Progress

• April 1986 - The term high-temperature superconductor was first used to designate the new family of cuprate-perovskite ceramic materials discovered by Johannes Georg Bednorz and Karl Alexander Müller, for which they won the Nobel Prize in Physics the following year. Their discovery of the first high-temperature superconductor, LaBaCuO, with a transition temperature of 35 K, generated great excitement.

• LSCO (La_2-xSr_xCuO₂) discovered the same year.

• January 1987 - YBCO was discovered to have a T_c of 90 K.

• 1988 - BSCCO discovered with T_c up to 107 K, and TBCCO (T=thallium) discovered to have T_c of 125 K.

• As of 2009, the highest-temperature superconductor (at ambient pressure) is mercury barium calcium copper oxide (HgBa₂Ca₂Cu₃O_x), at 138 K and is held by a cuprate-perovskite material, possibly 164 K under high pressure.

• Recently, other unconventional superconductors, not based on cuprate structure, have been discovered. Some have unusually high values of the critical temperature, T_c, and hence they are sometimes also called high-temperature superconductors.

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.