On April 8, 1911, at the Leiden Cryogenic Laboratory in the Netherlands, Heike Kamerlingh Onnes and his collaborators immersed a mercury capillary in liquid helium and saw the mercury's electrical resistance drop to nothing once the temperature reached about 3 kelvins, or 3 degrees above absolute zero (around –270 Celsius). This phenomenon of "superconductivity" was one of the first quantum phenomena to be discovered, although back then quantum theory did not exist. In subsequent decades theoreticians were able to put quantum physics on a solid foundation and explain superconductivity.
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