Mercury is the metal in which superconductivity was first observed. It had to be cooled to -269°C, really close to absolute zero. The best superconductor we have yet discovered becomes superconducting below -135°C. The physics of superconductors is hence closely linked to the study of very low temperatures accessible with specific cooling techniques, using cryogenic liquids such as liquid helium or nitrogen, and even more sophisticated tools.
At what temperature do we observe superconductivity ?
Superconductivity is actually observed only when it's colder than the coldest place on earth :
