Superconductivity The property of a substance in which the electrical resistance of the substance is zero at very low temperatures. This property of substance is called superconductivity. For certain substances, like mercury, the resistivity suddenly drops to zero at very low temperatures typically near the boiling point of liquid helium. Some metals, doped semiconductors, alloys and ceramics (i.e. these are insulators at room temperature and superconduct at higher temperatures than the metals) show superconductivity. Temperature Dependence of Resistivity In superconducting substances, the resistivity suddenly drops to zero at a particular temperature known as critical temperature ($T_{c}$) or transition temperature and remains zero below that as shown in Figure below. The critical temperature for mercury is $4.2 K$. Below this critical temperature, mercury is superconducting whereas above this temperature it behaves like a normal conductor. Different superconducting
(The Advance Learning Institute of Physics and Technology)