Supraleituvuuden

Supraleituvuuden is the phenomenon where certain materials exhibit zero electrical resistance when cooled below a characteristic critical temperature. This means that electric current can flow through them indefinitely without any energy loss. The discovery of supraleituvuuden was made by Heike Kamerlingh Onnes in 1911 while studying the electrical properties of mercury at very low temperatures. When the temperature of mercury dropped to about 4.2 Kelvin, its resistance vanished.

Beyond zero resistance, supraleituvuuden also involves the expulsion of magnetic fields from the interior of the superconductor, a property known as the Meissner effect. This effect is crucial for many applications of supraleituvuuden. Superconductors can be broadly classified into two types: Type I and Type II. Type I superconductors, like mercury, exhibit a sharp transition to the superconducting state and completely expel magnetic fields up to a critical magnetic field. Type II superconductors, on the other hand, allow magnetic fields to penetrate partially in the form of quantized flux lines above a lower critical magnetic field but remain superconducting up to a much higher upper critical magnetic field.

The theoretical explanation for conventional superconductivity was provided by the BCS theory, developed by John Bardeen, Leon Cooper, and Robert Schrieffer. This theory describes superconductivity as arising from the formation of Cooper pairs, where electrons are weakly bound together by lattice vibrations. The discovery of high-temperature superconductors in 1986, which exhibit superconductivity at significantly higher temperatures (though still very cold by everyday standards), opened up new avenues of research and potential applications. These high-temperature superconductors, often ceramic materials, are not fully explained by the BCS theory, leading to ongoing scientific investigation.