The Phenomenon of Superconductivity

While measuring the resistivity of mercury at low temperatures in 1911, Kamerlingh Onnes discovered that at a specific temperature (the critical temperature TC) the resistivity sharply falls to zero; the material enters the superconducting state. Defining properties of the superconducting state are zero-resistivity, the Meissner effect (perfect diamagnetism) and the energy gap in the density of states of electrons. Since their discovery many theories were developed in order to explain the phenomenon and they succeeded in doing so. In 1986, however, Bednorz and Muller discovered the superconducting state in cuprates with the surprisingly high critical temperature at around 80 K (at that time no known superconductors had the TC higher than 30 K). These superconductors (the high temperature superconductors) do not obey the existing theories and so either new theories must be developed or the existing ones adapted to explain the

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