Superconductivity

On this day in 1911, Dutch physicist Heike Kamerlingh Onnes discovered superconductivity—the flow of electricity with zero resistance. At the time Onnes was pursuing the question of what happens to metals when they are cooled to extremely low temperatures. Some physicists thought the electrical resistance would drop to zero; others thought the opposite would happen and current wouldn’t flow at all. To chill metal samples to nearly absolute zero, Onnes used liquid helium, which he had first produced in his Leiden University lab in 1908. On April 8, 1911, Onnes fired up the cryostat and measured the resistances of electrodes made of mercury and gold. At 4.3 K (–269 degrees Celsius) both metals still exhibited electrical resistance. But when the temperature dipped another 1.3 degrees, “Kwik nagenoeg nul,” Onnes wrote in his lab notebook: “Mercury[‘s resistance] practically zero.” Mercury became the first known superconductor. Since then physicists have found many other materials that exhibit superconductivity, but all require incredibly frigid temperatures. To learn more about Onnes’ Nobel-winning discovery (and his frustratingly sloppy handwriting), read “The discovery of superconductivity” from the September 2010 issue of Physics Today: http://goo.gl/DZXC3L

Date in History: 8 April 1911