High-temperature Superconductivity - History

History

The phenomenon of superconductivity was discovered by Kamerlingh Onnes in 1911, in metallic mercury below 4 K (−269.15 °C). 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 13 K (−260.2 °C), which were much higher than those for elemental metals. In 1987, K Alex Mueller and J. Georg Bednorz, working at the IBM research lab near Zurich, Switzerland were exploring a new class of ceramics for superconductivity. Bednorz encountered a compound of Lithium, Barium and Copper oxide whose resistance dropped down to zero at a temperature around 35 K (−238.2 °C). Their results were soon confirmed by two groups, 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.

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.

• April 1911 – Kamerlingh Onnes discovers superconductivity.
• 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 30 K, generated great excitement.

• LSCO (La_2-xSr_xCuO₄) 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 108 K, and TBCCO (T=thallium) discovered to have T_c of 127 K.

• As of 2009, the highest-temperature superconductor (at ambient pressure) is mercury barium calcium copper oxide (HgBa₂Ca₂Cu₃O_x), around 135 K and is held by a cuprate-perovskite material, which possibly reaches 164 K under high pressure.
• Recently, iron-based superconductors with critical temperatures as high as 56 K have been discovered. These are often also referred to as high-temperature superconductors.