Supersolid

In condensed matter physics, a supersolid is a spatially ordered (i.e. solid) material with superfluid properties. In the case of helium-4, it has been conjectured since the 1960s that it might be possible to create a supersolid.[1] Starting from 2017, a definitive proof for the existence of this state was provided by several experiments using atomic Bose–Einstein condensates.[2] The general conditions required for supersolidity to emerge in a certain substance are a topic of ongoing research.

## Contents

* 1 Background
* 2 Superglass
* 3 Experiments using helium
* 4 Experiments using ultracold quantum gases
* 5 Experiments using exciton-polaritons
* 6 Theory
* 7 See also
* 8 References

## Background

A supersolid is a special quantum state of matter where particles form a rigid, spatially ordered structure, but also flow with zero viscosity. This is in contradiction to the intuition that flow, and in particular superfluid flow with zero viscosity, is a property exclusive to the fluid state, e.g., superconducting electron and neutron fluids, gases with Bose–Einstein condensates, or unconventional liquids such as helium-4 or helium-3 at sufficiently low temperature. For more than 50 years it was thus unclear whether the supersolid state could exist.[3]

## Superglass

A superglass is a similar hypothetical phase of matter which is characterized by superfluidity and a frozen amorphous structure at the same time. This idea was put forward by Anthony James Leggett in 1970.[4] In 2009, it was theorised that frozen helium-4 (at 0.2 K and 50 atm) may be a superglass.[5][6][7]

## Experiments using helium

In the 1980s, the first anomaly in a solid was discovered by using ultrasound.[8] Further research detected supersolid behavior in 2004. Specifically, a non-classical rotational moment of inertia of a torsional oscillator was observed. This observation could not be explained by classical models but was consistent with superfluid-like behavior of a small percentage of the helium atoms contained within the oscillator.[9][4]

This observation triggered a large number of follow-up studies to reveal the role played by crystal defects or helium-3 impurities. Further experimentation has cast some doubt on the existence of a true supersolid in helium. Most importantly, it was shown that the observed phenomena could be largely explained due to changes in the elastic properties of the helium.[10] In 2012, the experiments that detected supersolid-like behavior in 2004 were repeated to eliminate any such contributions. No supersolid behavior was found in the repeated experiments.[11]

## Experiments using ultracold quantum gases

In 2017, supersolid properties were created in ultracold quantum gases via different methods. One placed a Bose–Einstein condensate inside two optical resonators, which enhanced the atomic interactions until they started to spontaneously crystallize and form a solid that maintains the inherent superfluidity of Bose–Einstein condensates. This setting realises a special form of a supersolid, the so-called lattice supersolid, where atoms are pinned to the sites of an externally imposed lattice structure.[12][13]

The other method exposed a Bose–Einstein condensate in a double-well potential to light beams that created an effective spin–orbit coupling. The interference between the atoms on the two spin–orbit coupled lattice sites gave rise to a characteristic density modulation.[14][15]

In 2019, supersolid properties in dipolar Bose–Einstein condensates formed from lanthanide atoms were independently observed by three research groups.[16] In these systems, supersolidity emerges directly from the atomic interactions, without the need for an external optical lattice. This also allowed the direct observation of superfluid flow and hence the definitive proof for the existence of the supersolid state of matter.[17][18]

In 2021, confocal cavity quantum electrodynamics with a Bose–Einstein condensate were used to create a supersolid that possesses a key property of solids, vibration. That is, a supersolid was created that possesses lattice phonons with a Goldstone mode dispersion exhibiting a 16 cm/s (6.3 in/s) speed of sound.[19]

In 2021, dysprosium was used to create a 2-dimensional supersolid quantum gas, in 2022, the same team created a supersolid disk in a round trap and in 2024 they reported the observation of quantum vortices in the supersolid phase.[20][21][22][23]

## Experiments using exciton-polaritons

In 2025, supersolid behaviour was observed in an exciton–polariton condensate formed in a photonic-crystal waveguide, showing that supersolidity can emerge in a driven-dissipative, non-equilibrium solid-state platform.[24] In 2026, a room-temperature exciton–polariton supersolid was demonstrated in a halide-perovskite nanophotonic structure.[25] Together, these studies established exciton–polariton systems as an new platform for the study of supersolidity, complementary to the ultracold atomic gases.

## Theory

In most theories of this state, it is supposed that vacancies – empty sites normally occupied by particles in an ideal crystal – lead to supersolidity. These vacancies are caused by zero-point energy, which also causes them to move from site to site as waves. Because vacancies are bosons, if such clouds of vacancies can exist at very low temperatures, then a Bose–Einstein condensation of vacancies could occur at temperatures less than a few tenths of a Kelvin. A coherent flow of vacancies is equivalent to a "superflow" (frictionless flow) of particles in the opposite direction. Despite the presence of the gas of vacancies, the ordered structure of a crystal is maintained, although with less than one particle on each lattice site on average. Alternatively, a supersolid can also emerge from a superfluid. In this situation, which is realised in the experiments with atomic Bose–Einstein condensates, the spatially ordered structure is a modulation on top of the superfluid density distribution.

## See also

* Superfluid film
* Superglass
* Quasi-solid

## References

1. ↑ Chester, G. V. (1970). "Speculations on Bose–Einstein Condensation and Quantum Crystals". Physical Review A 2 (1): 256–258. doi:10.1103/PhysRevA.2.256. Bibcode: 1970PhRvA...2..256C.
2. ↑ Donner, Tobias (2019-04-03). "Viewpoint: Dipolar Quantum Gases go Supersolid". Physics 12: 38. doi:10.1103/Physics.12.38.
3. ↑ Balibar, Sebastien (March 2010). "The enigma of supersolidity". Nature 464 (7286): 176–182. doi:10.1038/nature08913. PMID 20220834. Bibcode: 2010Natur.464..176B.
4. ↑ 4.0 4.1 Leggett, A. J. (1970-11-30). "Can a Solid Be "Superfluid"?". Physical Review Letters 25 (22): 1543–1546. doi:10.1103/PhysRevLett.25.1543. Bibcode: 1970PhRvL..25.1543L.
5. ↑ "Press release: Supersolid or superglass? Cornell researchers study a strange state of matter in helium - Cornell Chronicle". https://news.cornell.edu/stories/2009/04/frozen-helium-4-may-be-unusual-superglass.
6. ↑ Yu, Xiaoquan; Mueller, Markus (2012). "Mean field theory of superglasses". Physical Review B 85 (10). doi:10.1103/PhysRevB.85.104205. Bibcode: 2012PhRvB..85j4205Y.
7. ↑ Giulio Biroli; Claudio Chamon; Francesco Zamponi (2008). "Theory of the superglass phase". Physical Review B 78 (22): 19. doi:10.1103/PhysRevB.78.224306. Bibcode: 2008PhRvB..78v4306B.
8. ↑ Chalmers, Matthew (2007-05-01). "The quantum solid that defies expectation". Physics World. https://physicsworld.com/a/the-quantum-solid-that-defies-expectation.
9. ↑ Kim, E.; Chan, M. H. W. (2004). "Probable Observation of a Supersolid Helium Phase". Nature 427 (6971): 225–227. doi:10.1038/nature02220. PMID 14724632. Bibcode: 2004Natur.427..225K.
10. ↑ Day, James; Beamish, John (December 2007). "Low-temperature shear modulus changes in solid 4 He and connection to supersolidity". Nature 450 (7171): 853–856. doi:10.1038/nature06383. PMID 18064007. Bibcode: 2007Natur.450..853D.
11. ↑ Voss, David (2012-10-08). "Focus: Supersolid Discoverer's New Experiments Show No Supersolid". Physics 5: 111. doi:10.1103/physics.5.111. Bibcode: 2012PhyOJ...5..111V.
12. ↑ Würsten, Felix (1 March 2017). "Crystalline and liquid at the same time". ETH Zurich. https://www.ethz.ch/content/main/en/news-und-veranstaltungen/eth-news/news/2017/03/Kristallin-und-fluessig-zugleich.html.
13. ↑ Léonard, Julian; Morales, Andrea; Zupancic, Philip; Esslinger, Tilman; Donner, Tobias (1 March 2017). "Supersolid formation in a quantum gas breaking a continuous translational symmetry". Nature 543 (7643): 87–90. doi:10.1038/nature21067. PMID 28252072. Bibcode: 2017Natur.543...87L.
14. ↑ Keller, Julia C. (March 2, 2017). "MIT researchers create new form of matter". MIT News. https://news.mit.edu/2017/mit-researchers-create-new-form-matter-0302.
15. ↑ Li, Jun-Ru; Lee, Jeongwon; Huang, Wujie; Burchesky, Sean; Shteynas, Boris; Top, Furkan Çağrı; Jamison, Alan O.; Ketterle, Wolfgang (1 March 2017). "A stripe phase with supersolid properties in spin–orbit-coupled Bose–Einstein condensates". Nature 543 (7643): 91–94. doi:10.1038/nature21431. PMID 28252062. Bibcode: 2017Natur.543...91L.
16. ↑ Donner, Tobias (April 3, 2019). "Viewpoint: Dipolar Quantum Gases go Supersolid". APS Physics. http://physics.aps.org/articles/v12/38.
17. ↑ Guo, Mingyang; Böttcher, Fabian; Hertkorn, Jens; Schmidt, Jan-Niklas; Wenzel, Matthias; Büchler, Hans Peter; Langen, Tim; Pfau, Tilman (October 2019). "The low-energy Goldstone mode in a trapped dipolar supersolid". Nature 574 (7778): 386–389. doi:10.1038/s41586-019-1569-5. PMID 31499511. Bibcode: 2019Natur.574..386G.
18. ↑ Tanzi, L.; Roccuzzo, S. M.; Lucioni, E.; Famà, F.; Fioretti, A.; Gabbanini, C.; Modugno, G.; Recati, A. et al. (October 2019). "Supersolid symmetry breaking from compressional oscillations in a dipolar quantum gas". Nature 574 (7778): 382–385. doi:10.1038/s41586-019-1568-6. PMID 31499510. Bibcode: 2019Natur.574..382T.
19. ↑ Guo, Yudan; Kroeze, Ronen M.; Marsh, Brendan P.; Gopalakrishnan, Sarang; Keeling, Jonathan; Lev, Benjamin L. (2021). "An optical lattice with sound". Nature 599 (7884): 211–215. doi:10.1038/s41586-021-03945-x. PMID 34759361. Bibcode: 2021Natur.599..211G.
20. ↑ Norcia, Matthew A.; Politi, Claudia; Klaus, Lauritz; Poli, Elena; Sohmen, Maximilian; Mark, Manfred J.; Bisset, Russell N.; Santos, Luis et al. (August 2021). "Two-dimensional supersolidity in a dipolar quantum gas". Nature 596 (7872): 357–361. doi:10.1038/s41586-021-03725-7. PMID 34408330. Bibcode: 2021Natur.596..357N.
21. ↑ Bland, Thomas; Poli, Elena; Politi, Claudia; Lauritz, Klaus; Norcia, Matthew A.; Ferlaino, Francesca; Santos, Luis; Bisset, Russell N. (13 May 2022). "Two-dimensional supersolidity in a circular trap". Phys. Rev. Lett. 128 (19). doi:10.1103/PhysRevLett.128.195302. PMID 35622047.
22. ↑ Casotti, Eva; Poli, Elena; Klaus, Lauritz; Litvinov, Andrea; Ulm, Clemens; Politi, Claudia; Mark, Manfred J.; Bland, Thomas et al. (2024). "Observation of vortices in a dipolar supersolid". Nature 635 (8038): 327–331. doi:10.1038/s41586-024-08149-7. ISSN 0028-0836. PMID 39506121. Bibcode: 2024Natur.635..327C. https://www.nature.com/articles/s41586-024-08149-7.
23. ↑ Savitsky, Zack (2024-11-06). "Physicists Spot Quantum Tornadoes Twirling in a 'Supersolid'" (in en). https://www.quantamagazine.org/physicists-spot-quantum-tornadoes-twirling-in-a-supersolid-20241106/.
24. ↑ Trypogeorgos, Dimitrios; Gianfrate, Antonio; Landini, Manuele; Nigro, Davide; Gerace, Dario; Carusotto, Iacopo; Riminucci, Fabrizio; Baldwin, Kirk et al. (2025). "Emerging supersolidity in photonic-crystal polariton condensates". Nature 639: 337–341. https://www.nature.com/articles/s41586-025-08616-9.
25. ↑ Meng, Yilin; Li, Wei; Peng, Kai; Ti, Chaoyang; Dang, Jianchen; Wu, Xiaolong; Han, Xu; Bao, Wei (2026). "Hybrid perovskite–nanograting photonic architecture enables supersolidity at room temperature". Nature Nanotechnology. doi:10.1038/s41565-026-02141-0. https://www.nature.com/articles/s41565-026-02141-0.

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States of matter (list)

State|

* Solid
* Liquid
* Gas / Vapor
* Plasma

Low energy|

* Bose–Einstein condensate
* Fermionic condensate
* Degenerate matter
* Quantum Hall
* Rydberg matter
* Rydberg polaron
* Strange matter
* Superfluid
* Supersolid
* Photonic matter

High energy|

* QCD matter
* Lattice QCD
* Quark–gluon plasma
* Color-glass condensate
* Supercritical fluid

Other states|

* Colloid
* Glass
* Crystal
* Liquid crystal
* Time crystal
* Quantum spin liquid
* Exotic matter
* Programmable matter
* Dark matter
* Antimatter
* Magnetically ordered
* Antiferromagnet
* Ferrimagnet
* Ferromagnet
* String-net liquid
* Superglass

Transitions|

* Boiling
* Boiling point
* Condensation
* Critical line
* Critical point
* Crystallization
* Deposition
* Evaporation
* Flash evaporation
* Freezing
* Chemical ionization
* Ionization
* Lambda point
* Melting
* Melting point
* Recombination
* Regelation
* Saturated fluid
* Sublimation
* Supercooling
* Triple point
* Vaporization
* Vitrification

Quantities|

* Enthalpy of fusion
* Enthalpy of sublimation
* Enthalpy of vaporization
* Latent heat
* Latent internal energy
* Trouton's ratio
* Volatility

Concepts|

* Baryonic matter
* Binodal
* Compressed fluid
* Cooling curve
* Equation of state
* Leidenfrost effect
* Macroscopic quantum phenomena
* Mpemba effect
* Order and disorder
* Spinodal
* Superconductivity
* Superheated vapor
* Superheating
* Thermo-dielectric effect

* v
* t
* e

States of matter (list)

State|

* Solid
* Liquid
* Gas / Vapor
* Plasma

Low energy|

* Bose–Einstein condensate
* Fermionic condensate
* Degenerate matter
* Quantum Hall
* Rydberg matter
* Rydberg polaron
* Strange matter
* Superfluid
* Supersolid
* Photonic matter

High energy|

* QCD matter
* Lattice QCD
* Quark–gluon plasma
* Color-glass condensate
* Supercritical fluid

Other states|

* Colloid
* Glass
* Crystal
* Liquid crystal
* Time crystal
* Quantum spin liquid
* Exotic matter
* Programmable matter
* Dark matter
* Antimatter
* Magnetically ordered
* Antiferromagnet
* Ferrimagnet
* Ferromagnet
* String-net liquid
* Superglass

Transitions|

* Boiling
* Boiling point
* Condensation
* Critical line
* Critical point
* Crystallization
* Deposition
* Evaporation
* Flash evaporation
* Freezing
* Chemical ionization
* Ionization
* Lambda point
* Melting
* Melting point
* Recombination
* Regelation
* Saturated fluid
* Sublimation
* Supercooling
* Triple point
* Vaporization
* Vitrification

Quantities|

* Enthalpy of fusion
* Enthalpy of sublimation
* Enthalpy of vaporization
* Latent heat
* Latent internal energy
* Trouton's ratio
* Volatility

Concepts|

* Baryonic matter
* Binodal
* Compressed fluid
* Cooling curve
* Equation of state
* Leidenfrost effect
* Macroscopic quantum phenomena
* Mpemba effect
* Order and disorder
* Spinodal
* Superconductivity
* Superheated vapor
* Superheating
* Thermo-dielectric effect

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