The atoms in materials vibrate due to thermal energy contained in the materials: the higher the temperature, the more the atoms vibrate. An ordinary conductor’s electrical resistance is caused by these atomic vibrations, which obstruct the movement of the electrons forming the current. Using the Kelvin ^27, or absolute, scale of temperature, 0K (corresponding to –273^o C) is the coldest possible temperature and is known as absolute zero. If an ordinary conductor were to be cooled to a temperature of absolute zero, atomic vibrations would cease, electrons would flow without obstruction, and electrical resistance would fall to zero. A temperature of absolute zero cannot be achieved in practice, but some materials exhibit superconducting characteristics at higher temperatures.²⁸

In 1911, the Dutch physicist Heike Kamerlingh Onnes discovered superconductivity in mercury at a temperature of approximately 4 K (-269^o C). Many other superconducting metals and alloys were subsequently discovered but, until 1986, the highest temperature at which superconducting properties were achieved was around 23 K (-250^o C) with the niobium-germanium alloy (Nb₃Ge)

In 1986 Georg Bednorz and Alex Muller discovered a metal oxide that exhibited superconductivity at the relatively high temperature of 30 K (-243^o C). This led to the discovery of ceramic oxides that superconduct at even higher temperatures. In 1988, and oxide of thallium, calcium, barium and copper (Ti²Ca²Ba₂Cu₃O₁₀) displayed superconductivity at 125 K (-148^o C), and, in 1993 a family based on copper oxide and mercury attained superconductivity at 160 K (-113^o C). These “high-temperature” superconductors are all the more noteworthy because ceramics are usually extremely good insulators.