Heike Kamerlingh Onnes

Heike Kamerlingh Onnes was a Dutch physicist who pioneered low-temperature physics, first liquefied helium in 1908, and discovered superconductivity in 1911.

Superconductivity: The state in which certain materials exhibit zero electrical resistance and expel magnetic fields below a critical temperature. Onnes discovered this state in mercury cooled near the temperature of liquid helium.
Liquid helium: Helium in its liquid state, used to reach temperatures near absolute zero. Onnes first produced it in 1908, providing the cooling medium for his superconductivity experiments.
Low-temperature physics: The study of physical phenomena at temperatures far below ordinary environmental conditions. Onnes established a leading experimental program in this field at Leiden.
Residual resistance: The nonzero electrical resistance that remains in a material as its temperature approaches absolute zero. Ordinary metals retain residual resistance, unlike the abrupt zero-resistance state Onnes found in mercury.
Nobel Prize in Physics: An annual international award recognizing major contributions to physics. Onnes received the 1913 prize for investigations into the properties of matter at low temperatures.
Joule–Thomson effect: The temperature change of a real gas as it expands through a porous plug without exchanging heat. Gas liquefaction systems exploit this cooling effect, central to the methods refined in Onnes’s laboratory.
Johannes Diderik van der Waals: A Dutch physicist known for an equation of state describing real gases and liquids. Van der Waals supervised Onnes’s doctoral research on the continuity of gaseous and liquid states.
Meissner effect: The expulsion of magnetic flux from a material as it enters the superconducting state. Discovered after Onnes, it showed that superconductivity is more than merely zero electrical resistance.
Leiden University: A Dutch research university founded in 1575 in the city of Leiden. Onnes built the cryogenic laboratory there that enabled his landmark experiments.
Kelvin scale: An absolute temperature scale whose zero is absolute zero. Onnes’s low-temperature measurements and discoveries are expressed in kelvins.

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