On April 8, 1911, during a study of the resistance of solid mercury at very cold temperatures, superconductivity was discovered by Heike Kamerlingh Onnes. Electrical resistance, a sort of electric friction, results in heat loss. Scientists had begun believing in the late 1800s that low temperatures could result in a reduction or lack of electrical resistance, but it was not until Onnes produced liquid helium in 1908 that more in-depth research could be performed. Using his newly discovered liquid helium, Onnes began looking at the resistance of platinum and gold at cold temperatures, but it was the use of mercury that proved successful. As the temperature of the liquid helium decreased, so did the resistance of the mercury, until the temperature of 4.19 Kelvin, when the resistance disappeared. A total lack of electrical resistance became known as superconductivity.
Most substances cannot superconduct, but the ones that can are known as superconductors. As temperatures drop, the superconductor experiences less and less electrical resistance, until reaching a certain temperature when resistance disappears and the superconductor undergoes a phase change. Types of superconductors are established based on their response to magnetic fields, critical temperatures, and materials. Magnetism is an integral part of superconductivity and it works because of the Meissner effect, where a superconductor expels its magnetic field.
Superconductivity is used in a variety of applications. MRI and NMR machines use superconducting magnets to create medical images. High-energy particle acceleration requires the use of superconductor magnets. Superconducting magnets are also used in maglev trains, such as the Shanghai Maglev Train in China and SCMaglev in Japan. Electric generators use superconducting wires to be more efficient and reduce heat loss.
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Superconductivity by Charles P Poole; et al
Superconductivity by V L Ginzburg; E A Andriushin
Superconductivity by J B Ketterson; S N Song