Superconductivity

Superconductivity is the complete disappearance of electrical resistance in certain materials, which occurs when they are cooled below a characteristic transtition temperature, T_C. Superconductivity was discovered in 1911, but initially, superconductivity was known to occur only at extremely low temperatures (T_C <= 23 K). Since the description of high temperaturs superconductivity in 1986, the highest temperatures at which superconductivity has been observed have increased steadily and the current record is around 133 K.

Superconductors are...

Some technological innovations benefiting from the discovery of superconductivity include sensitive detectors for magnetic fields called SQUIDs, logic devices, Magnetic Resonance Imaging, beam-steering magnets in particle accelerators, and microwave filters (e.g., for mobile phone base stations). Promising future industrial and commercial applications include power cables, transformers, power storage, motors, and magnetic levitation devices.

Historical highlights

• 1911

Superconductivity is discovered by Heike Kammerlingh Onnes in mercury at temperatures less than 4 K.

• 1957

John Bardeen, Leon Cooper and Robert Schrieffer put forth a successful theory of superconductivity (now called the BCS theory).

• 1986

Superconductivity at about T_C=30 K is discovered by Bednorz and Müller (from IBM Zürich) in oxides. The phenomenon is termed high temperature superconductivity (HTSC).

• 1987

First HTSC with T_C>77 K. This makes it possible to cool the superconductors with liquid N₂. This is highly significant, because liquid nitrogen is far less expensive to purchase than liquid helium which was previously required to cool materials down to their superconducting range.

• 1993

Record critical temperature: T_C=133 K in a Hg-Ba-Ca-Cu-O system.

• 2001

Superconductivity at nearly T_C=40 K is discovered in the simple system of magnesium diboride. The result was reported at a conference in January, and has sparked a huge activity in the research community.