superfluidity

{{Main|Superfluid helium-4}}

Superfluidity was discovered in helium-4 by Pyotr Kapitsa{{cite journal|last1=Kapitza|first1=P.|date=1938|title=Viscosity of Liquid Helium Below the λ-Point|journal=Nature|volume=141|issue=3558|page=74|bibcode=1938Natur.141...74K|doi=10.1038/141074a0|s2cid=3997900|doi-access=free}} and independently by John F. Allen and Don Misener{{cite journal|last1=Allen|first1=J. F.|last2=Misener|first2=A. D.|date=1938|title=Flow of Liquid Helium II|journal=Nature|volume=142|issue=3597|page=643|bibcode=1938Natur.142..643A|doi=10.1038/142643a0|s2cid=4135906}} in 1937. Onnes possibly observed the superfluid phase transition on August 2 1911, the same day that he observed superconductivity in mercury.{{Cite journal |last1=van Delft |first1=Dirk |last2=Kes |first2=Peter |date=2010-09-01 |title=The discovery of superconductivity |url=https://pubs.aip.org/physicstoday/article/63/9/38/386608/The-discovery-of-superconductivityA-century-ago |journal=Physics Today |language=en |volume=63 |issue=9 |pages=38–43 |doi=10.1063/1.3490499 |bibcode=2010PhT....63i..38V |issn=0031-9228|doi-access=free }} It has since been described through phenomenology and microscopic theories.

In liquid helium-4, the superfluidity occurs at far higher temperatures than it does in helium-3. Each atom of helium-4 is a boson particle, by virtue of its integer spin. A helium-3 atom is a fermion particle; it can form bosons only by pairing with another particle like itself, which occurs at much lower temperatures. The discovery of superfluidity in helium-3 was the basis for the award of the 1996 Nobel Prize in Physics. This process is similar to the electron pairing in superconductivity.

Superfluidity in an ultracold fermionic gas was experimentally proven by Wolfgang Ketterle and his team who observed quantum vortices in lithium-6 at a temperature of 50 nK at MIT in April 2005.{{cite web| website=mit.edu |url = http://web.mit.edu/newsoffice/2005/matter.html| title = MIT physicists create new form of matter| date=22 June 2005 | access-date = November 22, 2010}}{{Cite journal | last1 = Grimm | first1 = R. | title = Low-temperature physics: A quantum revolution | doi = 10.1038/4351035a | journal = Nature | volume = 435 | issue = 7045 | pages = 1035–1036 | year = 2005 | pmid = 15973388|bibcode = 2005Natur.435.1035G | s2cid = 7262637 | doi-access = free }} Such vortices had previously been observed in an ultracold bosonic gas using rubidium-87 in 2000,{{Cite journal | last1 = Madison | first1 = K. | last2 = Chevy | first2 = F. | last3 = Wohlleben | first3 = W. | last4 = Dalibard | first4 = J. | title = Vortex Formation in a Stirred Bose–Einstein Condensate | doi = 10.1103/PhysRevLett.84.806 | journal = Physical Review Letters | volume = 84 | issue = 5 | pages = 806–809 | year = 2000 | pmid = 11017378|arxiv = cond-mat/9912015 |bibcode = 2000PhRvL..84..806M | s2cid = 9128694 }} and more recently in two-dimensional gases.{{Cite journal | last1 = Burnett | first1 = K. | title = Atomic physics: Cold gases venture into Flatland | doi = 10.1038/nphys704 | journal = Nature Physics | volume = 3 | issue = 9 | pages = 589 | year = 2007 |bibcode = 2007NatPh...3..589B | doi-access = free }} As early as 1999, Lene Hau created such a condensate using sodium atoms{{Cite journal | last1 = Hau | first1 = L. V. | last2 = Harris | first2 = S. E. | last3 = Dutton | first3 = Z. | last4 = Behroozi | first4 = C. H. | journal = Nature | volume = 397 | issue = 6720 | pages = 594–598| doi = 10.1038/17561 | year = 1999 |title=Light speed reduction to 17 metres per second in an ultracold atomic gas|bibcode = 1999Natur.397..594V | s2cid = 4423307 | url = http://nrs.harvard.edu/urn-3:HUL.InstRepos:3636967 | url-access = subscription }} for the purpose of slowing light, and later stopping it completely.{{cite web|url=http://www.physicscentral.com/explore/people/hau.cfm |title=Lene Hau |publisher= | website= Physicscentral.com |access-date=2013-02-10}} Her team subsequently used this system of compressed light{{Cite journal| url= https://groups.seas.harvard.edu/haulab/publications/pdf/HauScientificAmerican2003.pdf|title=Frozen Light|journal=Scientific American|pages=44–51|date=2003|first= Lene Vestergaard | last= Hau}} to generate the superfluid analogue of shock waves and tornadoes:{{cite web |url= http://www.siam.org/meetings/nw06/hau.php | title= Shocking Bose–Einstein Condensates with Slow Light | last=Hau| first= Lene |website= SIAM.org |publisher= Society for Industrial and Applied Mathematics | date= September 9–12, 2006}}

{{quote | These dramatic excitations result in the formation of solitons that in turn decay into quantized vortices—created far out of equilibrium, in pairs of opposite circulation—revealing directly the process of superfluid breakdown in Bose–Einstein condensates. With a double light-roadblock setup, we can generate controlled collisions between shock waves resulting in completely unexpected, nonlinear excitations. We have observed hybrid structures consisting of vortex rings embedded in dark solitonic shells. The vortex rings act as 'phantom propellers' leading to very rich excitation dynamics. | Lene Hau | SIAM Conference on Nonlinear Waves and Coherent Structures}}

The idea that superfluidity exists inside neutron stars was first proposed by Arkady Migdal.{{cite journal|author=A. B. Migdal|journal= Nucl. Phys. |volume=13|pages= 655–674 |date=1959|doi=10.1016/0029-5582(59)90264-0|title=Superfluidity and the moments of inertia of nuclei|issue=5|bibcode = 1959NucPh..13..655M }}{{cite journal|author=A. B. Migdal|journal= Soviet Phys. JETP |volume=10|page= 176 |date=1960|language=en|url=http://www.jetp.ac.ru/cgi-bin/e/index/e/10/1/p176?a=list|title=Superfluidity and the Moments of Inertia of Nuclei|issue= 5 |doi= 10.1016/0029-5582(59)90264-0 |bibcode= 1959NucPh..13..655M |url-access=subscription}} By analogy with electrons inside superconductors forming Cooper pairs because of electron–lattice interaction, it is expected that nucleons in a neutron star at sufficiently high density and low temperature can also form Cooper pairs because of the long-range attractive nuclear force and lead to superfluidity and superconductivity.{{cite book|author=U. Lombardo|author2=H.-J. Schulze|name-list-style=amp|series=Lecture Notes in Physics|title=Physics of Neutron Star Interiors|chapter=Superfluidity in Neutron Star Matter|volume=578|date=2001|pages=30–53|arxiv=astro-ph/0012209|doi=10.1007/3-540-44578-1_2|isbn=978-3-540-42340-9|s2cid=586149}}

{{Main|Superfluid vacuum theory}}

Superfluid vacuum theory (SVT) is an approach in theoretical physics and quantum mechanics where the physical vacuum is viewed as superfluid.{{Citation needed|date=March 2024}}

The ultimate goal of the approach is to develop scientific models that unify quantum mechanics (describing three of the four known fundamental interactions) with gravity. This makes SVT a candidate for the theory of quantum gravity and an extension of the Standard Model.{{Citation needed|date=March 2024}}

It is hoped that development of such a theory would unify into a single consistent model of all fundamental interactions,

and to describe all known interactions and elementary particles as different manifestations of the same entity, superfluid vacuum.{{Citation needed|date=March 2024}}

On the macro-scale a larger similar phenomenon has been suggested as happening in the murmurations of starlings. The rapidity of change in flight patterns mimics the phase change leading to superfluidity in some liquid states.{{cite journal |title=Information transfer and behavioural inertia in starling flocks |journal=Nature Physics |volume=10 |issue=9 |pages=615–698 |year=2014 |last1=Attanasi |first1=A. |last2=Cavagna |first2=A. |last3=Del Castello |first3=L. |last4=Giardina |first4=I. |last5=Grigera |first5=T. S. |last6=Jelić |first6=A. |last7=Melillo |first7=S. |last8=Parisi |first8=L. |last9=Pohl |first9=O. |last10=Shen |first10=E. |last11=Viale |first11=M. |doi=10.1038/nphys3035 |bibcode=2014NatPh..10..691A |pmid=25264452 |pmc=4173114 |arxiv=1303.7097}}

Light behaves like a superfluid in various applications such as Poisson's Spot. As the liquid helium shown above, light will travel along the surface of an obstacle before continuing along its trajectory. Since light is not affected by local gravity its "level" becomes its own trajectory and velocity. Another example is how a beam of light travels through the hole of an aperture and along its backside before diffraction.{{Citation needed|date=March 2024}}

• Boojum (superfluidity)
• Condensed matter physics
• Macroscopic quantum phenomena
• Quantum hydrodynamics
• Slow light
• Supersolid
• Two-fluid model

{{reflist}}

• {{Cite book|first=Isaac M.|last=Khalatnikov|title=An introduction to the theory of superfluidity|publisher=CRC Press |date=2018 |isbn=978-0-42-997144-0 |url=https://books.google.com/books?id=QXFQDwAAQBAJ}}
• {{Cite book|first=James F.|last=Annett |date=2005 |title=Superconductivity, superfluids, and condensates |publisher=Oxford Univ. Press |location=Oxford |isbn=978-0-19-850756-7 |url=https://books.google.com/books?id=WZcXmBrZIc8C}}
• Schmidt, A. (2015) [https://link.springer.com/book/10.1007/978-3-319-07947-9 Introduction to Superfluidity], Springer ISBN 978-3-319-0794
• {{Cite book|first=Tony|last=Guénault|title=Basic superfluids|publisher=Taylor & Francis|location=London |date=2003|isbn=0-7484-0891-6 |url=https://books.google.com/books?id=zTRAicK9G64C}}
• Svistunov, B. V., Babaev E. S., Prokof'ev N. V. [https://www.crcpress.com/Superfluid-States-of-Matter/Svistunov-Babaev-Prokofev/p/book/9781439802755 Superfluid States of Matter]
• {{Cite book|first=Grigory E.|last=Volovik|title=The Universe in a helium droplet |series=Int. Ser. Monogr. Phys. |volume=117 |date=2003 |pages=1–507 |isbn=978-0-19-850782-6 |url=https://books.google.com/books?id=0pEUDAAAQBAJ}}

• {{wikiquote-inline}}
• {{Commons category-inline|Superfluidity}}
• Video: [http://www.alfredleitner.com/p/liquid-helium.html Demonstration of superfluid helium] (Alfred Leitner, 1963, 38 min.)
• [https://physicsworld.com/a/superfluidity-seen-in-a-2d-fermi-gas/ Superfluidity seen in a 2d fermi gas] recent 2021 observation relevant for Cuprate superconductors

{{States of matter}}

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Category:Superfluidity

Category:Physical phenomena

Category:Fluid dynamics

Category:Liquid helium

Category:Phases of matter

Category:Lev Landau