Low temperature physics

Content

Low temperature physics is a branch of physics that studies the physical properties of systems at low temperatures. In particular, this section discusses phenomena such as superconductivity and superfluidity . Low-temperature physics studies physical processes that occur at very low temperatures, up to absolute zero , and studies the properties of materials at these low and ultra-low temperatures, and is thus associated with many fields of science and technology. ^[one]

Methods for obtaining low temperatures

Liquid Evaporation

To obtain and maintain low temperatures, liquefied gases are usually used. In a Dewar vessel containing liquefied gas that evaporates under atmospheric pressure, the constant normal boiling point of the refrigerant is fairly well maintained. The most commonly used refrigerants are liquid nitrogen and liquid helium . Previously used liquefied hydrogen and oxygen are now rarely used due to the increased explosion hazard of fumes. Nitrogen and helium are practically inert and the danger is only a sharp expansion during the transition from liquid to gaseous state.

By lowering the pressure above the free surface of the liquid, it is possible to obtain a temperature below the normal boiling point of this liquid. For example, by evacuating nitrogen vapors, one can achieve temperatures up to the triple point temperature of 63 K, evacuating hydrogen vapors (above the solid phase) can achieve a temperature of 10 K, evacuating helium vapors can achieve (under very good experimental conditions) a temperature of about 0.7 K.

Throttling

When flowing through the narrowing of the pipeline passageway, a throttle or through a porous baffle, gas or vapor pressure decreases along with a decrease in its temperature. The throttling effect is mainly used for deep cooling and gas liquefaction.

The temperature change with a small pressure change as a result of the Joule-Thomson process is determined by the derivative $\mu _{JT}=\left({\frac {\partial T}{\partial P}}\right)_{H}$ ${\ displaystyle \ mu _ {JT} = \ left ({\ frac {\ partial T} {\ partial P}} \ right) _ {H}}$ called the Joule-Thomson coefficient.

Extension with external work

It is possible to cool the gas using an expander, a device for additional cooling of the gas by its release under pressure into a cylinder with a piston, which moves with force. At the same time, the gas does the work and cools. Used in the liquid helium production cycle.

If you use a turbine instead of a piston, you will get a turboexpander whose principle of operation is similar.

Adiabatic demagnetization

The method is based on the effect of heat release from paramagnetic salts during their magnetization and subsequent absorption of heat during their demagnetization. This makes it possible to obtain temperatures up to 0.001 K. To obtain very low temperatures, salts with a low concentration of paramagnetic ions, that is, salts in which neighboring paramagnetic ions are separated by non-magnetic atoms, are most suitable.

Peltier Effect

The Peltier effect is used in thermoelectric cooling devices. It is based on lowering the temperature of semiconductor junctions when a constant electric current passes through them. The amount of heat generated and its sign depend on the type of contacting substances, the current strength and the time the current passes, that is, the amount of heat generated is proportional to the amount of charge passed through the contact.

Dissolution Cryostat

Dilution refrigerator

In the cooling process, a mixture of two helium isotopes is used : ³ He and ⁴ He . When cooled below 700 mK, the mixture undergoes spontaneous phase separation , forming phases rich in ³ He and rich in ⁴ He. The ³ He / ⁴ He mixture is liquefied in a condenser , which is connected via an inductor to the region of the ³ He rich mixing chamber. The ³ He atoms, passing through the phase boundary, take energy from the system. Continuous-cycle dilution refrigerators are commonly used in low-temperature physical experiments.

Low temperature measurement

The primary thermometric device for measuring thermodynamic temperature up to 1 K is a gas thermometer . Resistance thermometers are used ( platinum - for precision measurements, copper , coal ).

As secondary thermometers, thermocouples , semiconductor diodes can be used - however, they require graduation. An analogue of thermometry for saturated vapor pressure in the region of ultra-low temperatures is temperature measurement in the range of 30–100 mK using the osmotic pressure ³He in a mixture of ³He - ⁴ He.

History of Low Temperature Physics

The main stages in the development of low temperature physics were associated with the liquefaction of gases, which made it possible to carry out measurements at a temperature equal to the boiling point.

In 1852, James Joule and William Thomson discovered the Joule-Thomson effect .
In 1883, Sigismund Vrublevsky and Karol Olshevsky first received liquid oxygen and liquid nitrogen in measurable quantities.
In 1898, James Dewar produced about 20 cm³ of liquid hydrogen .
In 1908, Heike Kamerling-Onnes managed to get 60 cm³ of liquid helium . The low temperatures necessary for the condensation of helium were achieved with adiabatic throttling of hydrogen.
In 1913, Heike Kamerling-Onnes was awarded the Nobel Prize in Physics for receiving liquid helium.
In 1925, Albert Einstein theoretically predicted the existence of the Bose-Einstein Condensate as a consequence of the laws of quantum mechanics based on the works of Chatendranath Bose .
In 1926, Willem Hendrick Keyes was able to obtain 1 cm³ of solid helium, using not only low temperature, but also high pressure.
In 1930 ^[2], Willem Hendrick Keyes discovered the presence of a phase transition in liquid helium at a temperature of 2.17 K and a saturated vapor pressure of 0.005 MPa. Calls a phase stable above 2.17 K helium-I, and a phase stable below 2.17 K helium-II. He also observes the anomalies associated with this in thermal conductivity (he even calls helium II “super thermal conductive”), heat capacity, and helium flow.
In 1938, P.L. Kapitsa discovered the superfluidity of helium-II.
In 1941, a quantum-mechanical explanation of the phenomenon of superfluidity was given by L.D. Landau .
In 1948, for the first time, helium-3 was also liquefied. ^{[to whom?} ^]
In 1962, L.D. Landau received the Nobel Prize in Physics .
In 1972, a phase transition to a superfluid state was also detected in liquid ³ He. Later it was experimentally shown that below 2.6 mK and at a pressure of 34 atm ³ He really becomes superfluid.
In 1978, Peter Kapitsa , Arno Allan Penzias and Robert Woodrow Wilson received the Nobel Prize in Physics for the discovery of the phenomenon of superfluidity.
In 1995, Eric Cornell and Karl Wyman first received the Bose-Einstein Condensate . Scientists used gas from rubidium atoms, cooled to 170 nanokelvin .
In 1996, D. Osherov , R. Richardson, and D. Lee were awarded the Nobel Prize in Physics for the discovery of superfluidity of helium-3.
In 2001, Eric Cornell , Karl Wimann, and Wolfgang Ketterle were awarded the Nobel Prize in Physics for receiving the Bose - Einstein Condensate .
In 2003, the Nobel Prize in Physics was awarded to Aleksei Alekseevich Abrikosov , Vitalii Lazarevich Ginzburg and Anthony Legget , including for creating the theory of superfluidity of liquid helium-3.
In 2004, the discovery of superfluidity in solid helium was announced. This statement was made on the basis of the effect of an unexpected decrease in the moment of inertia of a torsion pendulum with solid helium. However, in subsequent years, the results of independent experiments could not confirm this discovery. The situation with superfluidity in solid helium remained unclear until 2012 , when it was shown that the interpretation of the discovered effect as the transition of solid helium to a superfluid state was erroneous.

VAK Specialty

“Low temperature physics” (specialty code 04/01/09) is a field of fundamental science that studies physical phenomena and states of matter that are characteristic of temperatures close to absolute zero . It includes theoretical and experimental studies of the structure and properties of matter in the ground quantum state and the physical nature and characteristics of various elementary excitations , as well as quantum cooperative phenomena such as superfluidity , superconductivity , Bose condensation , magnetic, charge and other types of ordering. ^{[3] The} passport of the specialty of the Higher Attestation Commission “Low Temperature Physics” provides for the following research areas:

Quantum liquids and crystals .
Superconducting systems, including high temperature superconductors .
Quantum gases, Bose-Einstein condensates.
Strongly correlated electronic and phonon systems.
Low-temperature magnetism: magnetic structures, phase transitions, magnetic resonance.
Low-dimensional quantum systems and disordered systems.
Mesoscopic systems.
The study of the mechanical, electrical, magnetic, optical, thermal and other physical properties of a substance at low temperatures.
Development of methods for obtaining and measuring low and ultra-low temperatures.

Scientific journals

" Low Temperature Physics" of the Physicotechnical Institute of Low Temperatures named after B. I. Verkina NAS of Ukraine ^[4]

Notes

↑ Low temperature physics. A brief historical outline. (inaccessible link)
↑ Science and Technology: Physics / SUPERFluidity
↑ Passport of the specialty of VAK
↑ Journal of Low Temperature Physics

[1] Low temperature physics. A brief historical outline. (inaccessible link)

[2] Science and Technology: Physics / SUPERFluidity

[3] Passport of the specialty of VAK

[4] Journal of Low Temperature Physics