http://www1.physik.tu-muenchen.de/~gammel/matpack/html/images/Physicists/t_Kammerlingh_Onnes_Heike.jpg
In the early 1900's a duch physicist by the name of Heike Kammerlingh Onnes (pictured above), discovered superconductivity. Before his discovery, Onnes had spent most of his scientific career studying extreme cold. The first step he took toward superconductivity was on July 10, 1908 when he liquified helium and cooled it to an astonishing 4 K, which is roughly the temperature of the background radiation in open space. Using this liquid helium, Onnes began experimenting with other materials and their properties when subjected to intense cold. In 1911, he began his research on the electrical properties of these same materials. It was known to Onnes that as materials, particularly metals, cooled, they exhibited less and less resistance. Bringing a mercury wire to as close to absolute zero as possible, Onnes observed that as the temperature dropped, so to did the resistance, until 4.2 K was reached. There resistance vanished and current flowed through the wire unhindered. Below is an approximate graph displaying resistance as a function of temperature for the experiment Onnes conducted with mercury:
http://www.physnet.uni-hamburg.de/home/vms/reimer/htc/pt2.html
Continuing with his experiments, Onnes discovered what he came to call "persistent currents," which were electrical currents that flowed continuously in a superconductor without a voltage to drive them. Additionally, the currents in superconductors flowed without dissipating energy, a fact that Onnes proved when he instigated a current in a conductor and found that a year later the current was still flowing and had not degraded! In 1913, Onnes was awarded the Nobel Prize for his discovery and the field of superconductors was officially created.