Editing Roton

{{Short description|Collective excitation in superfluid helium-4 (a quasiparticle)}}
{{Other uses}}
[[File:RotonDispersionRelation.svg|thumb|Roton dispersion relation, showing the quasiparticle energy E(p) as a function of momentum p. A quasiparticle with momentum generated in the local energy minimum is called a roton.]]
In [[theoretical physics]], a '''roton''' is an elementary excitation, or [[quasiparticle]], seen in [[superfluid helium-4]] and [[Bose–Einstein condensate]]s with long-range [[Dipole|dipolar interactions]] or [[Spin–orbit interaction|spin-orbit coupling]]. The [[dispersion relation]] of elementary excitations in this [[superfluid]] shows a [[linear]] increase from the origin, but exhibits first a maximum and then a minimum in [[energy]] as the [[momentum]] increases. Excitations with momenta in the linear region are called [[phonon]]s; those with momenta close to the minimum are called rotons. Excitations with momenta near the maximum are called [[Maxon excitation|maxon]]s.

The term "roton-like" is also used for the predicted [[Eigenmode|eigenmodes]] in 3D [[Metamaterial|metamaterials]] using beyond-nearest-neighbor coupling.<ref>{{cite journal |last1=Wang |first1=Ke |last2=Chen |first2=Yi |last3=Kadic |first3=Muamer |last4=Wang |first4=Changguo |last5=Wegener |first5=Martin |date=24 May 2022 |title=Nonlocal interaction engineering of 2D roton-like dispersion relations in acoustic and mechanical metamaterials |journal=Communications Materials |volume=3 |issue=1 |page=35 |bibcode=2022CoMat...3...35W |doi=10.1038/s43246-022-00257-z |doi-access=free |s2cid=248991736}}</ref><ref>{{cite journal |last1=Chen |first1=Yi |last2=Kadic |first2=Muamer |last3=Wegener |first3=Martin |date=2 June 2021 |title=Roton-like acoustical dispersion relations in 3D metamaterials |journal=Nature Communications |volume=12 |issue=1 |pages=3278 |bibcode=2021NatCo..12.3278C |doi=10.1038/s41467-021-23574-2 |pmc=8172548 |pmid=34078904}}</ref> The observation of such a "roton-like" dispersion relation was demonstrated under ambient conditions for both acoustic pressure waves in a channel-based metamaterial at audible frequencies and transverse elastic waves in a microscale metamaterial at ultrasound frequencies.<ref>{{Cite journal |last1=Iglesias Martínez |first1=Julio Andrés |last2=Groß |first2=Michael Fidelis |last3=Chen |first3=Yi |last4=Frenzel |first4=Tobias |last5=Laude |first5=Vincent |last6=Kadic |first6=Muamer |last7=Wegener |first7=Martin |date=2021-12-03 |title=Experimental observation of roton-like dispersion relations in metamaterials |journal=Science Advances |language=en |volume=7 |issue=49 |pages=eabm2189 |doi=10.1126/sciadv.abm2189 |issn=2375-2548 |pmc=8635434 |pmid=34851658|bibcode=2021SciA....7.2189I }}</ref>

==Models==
Originally, the roton spectrum was phenomenologically introduced by [[Lev Landau]] in 1947.<ref>Landau, L. D. (1947). On the theory of superfluidity of helium II. Physics-Uspekhi, 11(1), 91.</ref> Currently there exist [[Superfluid helium-4#Theory|models]] which try to explain the roton spectrum with varying degrees of success and fundamentality.<ref>{{Cite journal|title = Fingerprinting Rotons in a Dipolar Condensate: Super-Poissonian Peak in the Atom-Number Fluctuations|date = 26 June 2013|journal = Phys. Rev. Lett. |volume=110 |page=265302|doi = 10.1103/PhysRevLett.110.265302|arxiv = 1304.3605 |bibcode = 2013PhRvL.110z5302B |last1 = Bisset|first1 = R. N.|last2 = Blakie|first2 = P. B.|issue = 26|pmid = 23848891|s2cid = 24788775}}</ref><ref>{{Cite journal|title = Roton spectroscopy in a harmonically trapped dipolar Bose–Einstein condensate|date = Aug 15, 2012|journal = Phys. Rev. A |volume=86 |pages=021604 |doi = 10.1103/PhysRevA.86.021604|arxiv = 1206.2770 |bibcode = 2012PhRvA..86b1604B |last1 = Blakie|first1 = P. B.|last2 = Baillie|first2 = D.|last3 = Bisset|first3 = R. N.|issue = 2|s2cid = 119285430}}</ref> The requirement for any model of this kind is that it must explain not only the shape of the spectrum itself but also other related observables, such as the [[speed of sound]] and [[structure factor]] of [[superfluid helium-4]].  Microwave and Bragg spectroscopy has been conducted on helium to study the roton spectrum.<ref>{{Cite journal|title = Microwave Spectroscopy of Condensed Helium at the Roton Frequency|date = 4 Nov 2009|journal = Journal of Low Temperature Physics|doi = 10.1007/s10909-009-0025-6|bibcode = 2010JLTP..158..244R |last1 = Rybalko|first1 = A.|last2 = Rubets|first2 = S.|last3 = Rudavskii|first3 = E.|last4 = Tikhiy|first4 = V.|last5 = Poluectov|first5 = Y.|last6 = Golovashchenko|first6 = R.|last7 = Derkach|first7 = V.|last8 = Tarapov|first8 = S.|last9 = Usatenko|first9 = O.|volume = 158|issue = 1–2|pages = 244–249|s2cid = 120191282}}</ref>

==Bose–Einstein condensation==
[[Bose–Einstein condensation of quasiparticles|Bose–Einstein condensation]] of rotons has been also proposed and studied.<ref>{{Cite journal|title = The role of the condensate in the existence of phonons and rotons|date = December 1993|journal = Journal of Low Temperature Physics|doi = 10.1007/BF00692035|bibcode = 1993JLTP...93..861G |last1 = Glyde|first1 = Henry R.|volume = 93|issue = 5–6|pages = 861–878|s2cid = 122151606}}</ref> Its first detection has been reported in 2018.<ref>{{cite journal|last1=Chomaz|first1=L.|title=Observation of roton mode population in a dipolar quantum gas|journal=Nature Physics|date=2018|volume=14|issue=5|pages=442–446|doi=10.1038/s41567-018-0054-7|pmid=29861780|pmc=5972007|arxiv=1705.06914|bibcode=2018NatPh..14..442C}}</ref> Under specific conditions the roton minimum gives rise to a crystal solid-like structure called the [[supersolid]], as shown in experiments from 2019.<ref>{{cite journal |last1=Donner |first1=Tobias |title=Dipolar Quantum Gases go Supersolid |journal=Physics |date=3 April 2019 |volume=12 |pages=38 |doi=10.1103/Physics.12.38 |bibcode=2019PhyOJ..12...38D |doi-access=free }}</ref><ref>{{cite web | url=https://phys.org/news/2019-04-teams-independently-dipolar-quantum-gasses.html | title=Three teams independently show dipolar quantum gasses support state of supersolid properties }}</ref><ref>{{cite journal |last1=Henkel |first1=N. |last2=Nath |first2=R. |last3=Pohl |first3=T. |title=Three-Dimensional Roton Excitations and Supersolid Formation in Rydberg-Excited Bose-Einstein Condensates |journal=Physical Review Letters |date=11 May 2010 |volume=104 |issue=19 |pages=195302 |doi=10.1103/PhysRevLett.104.195302 |pmid=20866972 |arxiv=1001.3250 |bibcode=2010PhRvL.104s5302H |s2cid=14445701 }}</ref>

==See also==
* [[Superfluid]]
* [[Macroscopic quantum phenomena]]
* [[Bose–Einstein condensate]]

==References==
{{Reflist}}

== Bibliography ==
* {{cite journal |last1=Feynman |first1=R. P. |title=Superfluidity and Superconductivity |journal=Reviews of Modern Physics |date=1 April 1957 |volume=29 |issue=2 |pages=205–212 |doi=10.1103/RevModPhys.29.205 |bibcode=1957RvMP...29..205F |url=https://authors.library.caltech.edu/43047/ |access-date=1 July 2022 |archive-date=29 June 2023 |archive-url=https://web.archive.org/web/20230629192419/https://authors.library.caltech.edu/43047/ |url-status=dead }}

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[[Category:Quasiparticles]]
[[Category:Bose–Einstein condensates]]
[[Category:Superfluidity]]
[[Category:Lev Landau]]