Low temperature physics

The low temperature physics is a branch of physics that deals with operations in cold matter is concerned. The temperature range considered is close to absolute zero on the temperature scale, ie close to 0  Kelvin (−273.15 degrees Celsius ). There is no precisely defined temperature from which one speaks of low-temperature physics. However, experiments are mostly associated with the use of cryogenic liquids such as liquid nitrogen (boiling point: 77.4  K ) or liquid helium (boiling point: 4.21 K). Below 1 K one often speaks of ultra-low temperatures .

history

Fundamental discoveries were often associated with the achievement of ever lower temperatures (e.g. that of superconductivity ). Heike Kamerlingh Onnes is considered the founder of modern low-temperature physics , who first succeeded in liquefying helium in Leiden in 1908 . In 2017, Swiss physicists succeeded in cooling a chip to less than 3 mK over a period of seven hours.

Methods for reaching low temperatures

• Cooling circuit according to Carl von Linde , see countercurrent principle (process engineering)
• Gas liquefaction according to Carl von Linde, see Joule-Thomson effect
• Gas circuit cooling
• Evaporative cooling
  temperature range: a few 100 millikelvin.
• Cooling with the help of the Pomeranchuk effect.
  Temperature range: a few millikelvin.
• ³ He- ⁴ He segregation cooling
  Temperature range: a few millikelvin.
• Magnetic cooling
  Temperature range: a few millikelvin down to a few microkelvin (μK).
• Laser cooling , Sisyphus cooling
• Evaporative cooling

Processes at low temperatures

• Superconductivity
  Many substances lose their electrical resistance at low temperatures.
• Superfluidity
  ³ He and ⁴ He can flow without friction at sufficiently low temperatures.
• Bose-Einstein condensation

Measurement of low temperatures

So far, no method is known with which the thermodynamic value of the temperature can be measured directly. For this reason, the vapor pressure of liquefied gases (He, H ₂ , N _2, etc.) is primarily used to determine low temperatures . This happens with the currently valid temperature scale ITS-90 , which covers the range from 0.65 to 1350 K. For even lower temperatures there is the provisional PLTS-2000 scale, which goes down to 0.9 mK, the Néel temperature in solid ³ He. To measure the temperature , different primary thermometers or secondary thermometers can be used, depending on the measuring range and experimental possibilities .

literature

• Christian Enss, Siegfried Hunklinger : Low temperature physics. Springer, Berlin, Heidelberg 2000, ISBN 3540676740
• Guy K. White, Philip J. Meeson: Experimental Techniques in Low-Temperature Physics . Oxford University Press, ISBN 0-19-851427-1
• Kurt Mendelssohn: The quest for absolute zero - the meaning of low temperature physics. Taylor & Francis, London 1977, ISBN 0-85066-119-6
• Yasu Takano: Low temperature physics. AIP Press, Melville 2006, ISBN 0-7354-0347-3
• Jack W. Ekin: Experimental techniques for low-temperature measurements. Oxford Univ. Pr., Oxford 2007, ISBN 978-0-19-857054-7
• Christian Enss: Cryogenic particle detection. Springer, Berlin 2005, ISBN 3-540-20113-0
• Henk TC Stoof et al .: Ultracold quantum fields. Springer, Dordrecht 2009, ISBN 978-1-4020-8762-2

See also

• Nuclear magnetic resonance
• SQUID thermometry
• Noise thermometer
• Walther Meißner Institute for Low Temperature Research

Individual evidence

1. ↑ Swiss researchers break the cold record with Chip. In: science.orf.at. December 20, 2017, accessed November 1, 2018 .