How it began
Heike Kamerlingh Onnes, born in Groningen in 1853, was professor at Leiden University, where he ran a laboratory for low-temperature research. On July 10, 1908, he became the first to liquefy helium, which gave him temperatures within a few degrees of absolute zero. In April 1911, while measuring mercury cooled with liquid helium, he and his team saw its electrical resistance vanish abruptly at about 4.2 kelvin.
Before it existed
Physicists did not agree on what would happen to the resistance of a metal near absolute zero. One view held that it would fall slowly toward zero as the temperature dropped. Another held that it would level off at some constant value. Lord Kelvin believed that the electrons would freeze in place, so that the resistance would become infinite. No one could test these ideas until liquid helium made such temperatures reachable.
How it works
Below a critical temperature, certain materials carry electric current with no resistance at all, so a current once started keeps flowing without a power source. Onnes soon showed that tin and lead behave like mercury. By 1914 he had started a current in a ring of lead wire that was still flowing a year later. He first called the effect supraconductivity in 1913 and later changed the word to superconductivity.
What changed first
The first effect was on physics itself. Onnes received the Nobel Prize in Physics in 1913 for his investigations of matter at low temperatures, which led among other things to the production of liquid helium; the prize citation concerned the cold itself, and superconductivity was then a new and unexplained result. Liquid helium became the standard means of cooling substances in order to chart their properties at low temperature.
What lasted
A successful explanation took more than four decades: John Bardeen, Leon Cooper and Robert Schrieffer published their theory in 1957. In 1986 Georg Bednorz and Alex Müller discovered the first high-temperature superconductors. Superconductors are used today in magnetic resonance imaging machines, in high-energy physics, in levitating trains and in some electrical power applications.
