Suprasolidity

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The supersolid is a quantum mechanical state of matter, the same properties both solid as well as superfluid shows body. This condition was predicted as early as 1969 by David J. Thouless as well as Alexander Andrejew and Ilja Michailowitsch Lifschitz .

Researchers reported the first experimental evidence of the suprasolid state in 2004 using the example of ultra-cold solid helium-4 ( 4 He). However, it was only when the experiment was repeated in 2012 that the observed effect could be explained by the change in the elasticity of the solid helium. The existence of various forms of suprasolidity has been proven beyond doubt in experiments with Bose-Einstein condensates from 2017 . The general requirements and necessary properties for the creation of a supersolid are the subject of current research.

Experiment by Chan, Kim

Schematic structure of a torsional oscillator to demonstrate the suprasolidity

The experiments of Eun-Seong Kim and Moses HW Chan at the Pennsylvania State University with crystalline 4 He at temperatures below 200  mK with the help of a torsion oscillator provided the first experimental evidence for the existence of suprasolidity. In this experiment, the natural frequency of the torsional oscillator changed below about 200 mK, which was attributed to the fact that part of the crystalline 4 He had become superfluid. Measurements of the specific heat at the transition point to the rotational anomaly indicate a real phase transition . However, later studies showed that the change in the natural frequency can also be explained by an increase in the rigidity of the crystalline 4 He at low temperatures.

After the first publication of the observation of suprasolidity, other possible causes were also discussed heatedly and controversially in the specialist journals. An alternative explanation was a contamination with 3 He in the ppb range, which cannot be completely excluded , which is responsible for the superfluidity, while the crystalline structure can only be found in the 4 He species. A simultaneous occurrence of both phases (superfluid and solid) in the same atomic species would then not be given. Eventually, Chan's repetition of the experiment in 2012 refuted the original explanation of the observation as suprasolidity. The effect was attributed to elastic behavior due to dislocations in helium crystals. Although these cannot form in the Vycor nanopores, there is a possibility that there are larger cavities in which the possibility exists.

Experiments with Bose-Einstein condensates

In 2017 two groups reported on the realization of a super-solid in an optical lattice of ultra-cold atoms ( Bose-Einstein condensate ), one from ETH Zurich (headed by Tilman Esslinger ), the other from MIT (headed by Wolfgang Ketterle ). While in these experiments the crystal structure was induced by the optical lattice, in 2019 several groups (under the direction of Francesca Ferlaino , Tilman Pfau and Giovanni Modugno) succeeded in creating a super solid in which, as in helium, the interaction of the atoms alone was already possible led to the development of suprasolid properties. Here magnetic atoms with long-range dipole-dipole interaction played a decisive role. For certain strengths of this interaction, a lattice structure spontaneously formed on the superfluid Bose-Einstein condensate. In the experiments, both the spontaneous formation of the lattice structure and the superfluid flow of the atoms could be observed directly and thus the suprasolidity could be proven beyond doubt.

theory

Crystal defect (step dislocation)

Vacancies in 4 He crystals are considered to be a possible cause of suprasolidity in helium . It is discussed whether these crystal defects also exist essentially at absolute zero or whether they are based on experimentally used imperfect crystals. At sufficiently low temperatures, in suprasolid bodies such as in the Bose-Einstein condensate, the atoms are delocalized by superimposing their wave functions and thus also the vacancies in the crystal (quantum crystal), which could lead to the characteristic smooth flow. The suprasolidity thus represents a form of the Bose-Einstein condensate analogous to the Bose gas and the superfluidity.

An analogy to supersolidity in magnetic phase diagrams of anisotropic antiferromagnets in the field was shown in 1956 by Takeo Matsubara and H. Matsuda.

Bose-Einstein condensates were also used in experiments with ultra-cold atoms. In these, either through spin-orbit coupling, light fields in optical resonators or magnetic dipole-dipole interaction, rotonic excitation spectra were generated. This allows the Bose-Einstein condensate to develop a periodic density modulation that is equivalent to a lattice structure.

literature

  • AJ Leggett: Can a Solid be “Superfluid”? , Phys. Rev. Lett. 25: 1543 (1970); doi : 10.1103 / PhysRevLett.25.1543 .
  • GV Chester: Speculations on Bose-Einstein Condensation and Quantum Crystals , Phys. Rev. A 2, 256 (1970); doi : 10.1103 / PhysRevA.2.256 .
  • S. Balibar: The enigma of supersolidity . In: Nature . 464, No. 7286, March 2010, pp. 176-82. doi : 10.1038 / nature08913 . PMID 20220834 .
  • N. Prokof'ev: What makes a crystal supersolid? . In: Adv. Phys. . 56, 2007, pp. 381-402.
  • S. Balibar, F. Caupin: Supersolidity and disorder . In: J. Phys. Condens. Matter . 20 ,, 2008, p. 173201.
  • DE Galli, L. Reatto: Solid 4 He and the supersolid phase: from theoretical speculation to the discovery of a new state of matter? A review of the past and present status of research . In: J. Phys. Soc. Jpn . 77, 2008, p. 111010.

Web links

Individual evidence

  1. ^ DJ Thouless: The flow of a dense superfluid . In: Ann. Phys. . 51, 1969, pp. 403-427.
  2. ^ AF Andreev, IM Lifshitz: Quantum theory of defects in crystals . In: Sov. Phys. JETP . 29, 1969, pp. 1107-1113.
  3. ↑ E. Kim, MH Chan: Observation of superflow in solid helium . In: Science . 305, No. 5692, September 2004, pp. 1941-4. doi : 10.1126 / science.1101501 . PMID 15345778 .
  4. ↑ E. Kim, MH Chan: Probable observation of a supersolid helium phase . In: Nature . 427, No. 6971, January 2004, pp. 225-7. doi : 10.1038 / nature02220 . PMID 14724632 .
  5. ^ DY Kim, MHW Chan: Absence of Supersolidity in Solid Helium in Porous Vycor Glass ". Physical Review Letters, Volume 109, 2012, p. 155301. PMID 23102323
  6. ↑ Focus: Supersolid Discoverer's New Experiments Show No Supersolid, APS Physics 2012
  7. ↑ Julia Keller, MIT researchers create new form of matter, MIT News, March 2, 2017
  8. ↑ a b c Tobias Donner: Viewpoint: Dipolar Quantum Gases go Supersolid . In: Physics . tape April 12 , 2019 ( aps.org [accessed April 19, 2019]).
  9. ^ X. Lin, AC Clark, MH Chan: Probable heat capacity signature of the supersolid transition . In: Nature . 449, No. 7165, October 2007, pp. 1025-8. doi : 10.1038 / nature06228 . PMID 17960238 .
  10. ↑ J. Day, J. Beamish: Low-temperature shear modulus changes in solid 4He and connection to supersolidity . In: Nature . 450, No. 7171, December 2007, pp. 853-6. doi : 10.1038 / nature06383 . PMID 18064007 .
  11. ↑ E. Kim, JS Xia, JT West, X. Lin, AC Clark, MH Chan: Effect of 3He impurities on the nonclassical response to oscillation of solid 4He . In: Phys. Rev. Lett. . 100, No. 6, February 2008, p. 065301. PMID 18352487 .
  12. ↑ This source of error was first pointed out by James Day and John Beamish. Day, Beamish, Low-Temperature Shear Modulus Changes in Solid 4He and Connection to Supersolidity, Nature, Volume 450, 2007, p. 853
  13. ↑ a b Julian Léonard, Andrea Morales, Philip Zupancic, Tilman Esslinger, Tobias Donner: Supersolid formation in a quantum gas breaking a continuous translational symmetry, Nature, Volume 543, 2017, pp. 87-90
  14. ↑ a b Jun-Ru Li, Jeongwon Lee, Jeongwon, Wujie Huang, Sean Burchesky, Sean, Boris Shteynas, Furkan Çağrı Top, Alan O. Jamison, Wolfgang Ketterle: A stripe phase with supersolid properties in spin – orbit-coupled Bose– Einstein condensates, Nature, Volume 543, 2017, pp. 91-94
  15. ↑ Mingyang Guo, Fabian Böttcher, Jens Hertkorn, Jan-Niklas Schmidt, Matthias Wenzel: The low-energy Goldstone mode in a trapped dipolar supersolid . In: Nature . tape 574 , no. 7778 , October 2019, ISSN  1476-4687 , p. 386–389 , doi : 10.1038 / s41586-019-1569-5 ( nature.com [accessed November 1, 2019]).
  16. ↑ L. Tanzi, SM Roccuzzo, E. Lucioni, F. Famà, A. Fioretti: Supersolid symmetry breaking from compressional oscillations in a dipolar quantum gas . In: Nature . tape 574 , no. 7778 , October 2019, ISSN  1476-4687 , p. 382–385 , doi : 10.1038 / s41586-019-1568-6 ( nature.com [accessed November 1, 2019]).
  17. ↑ G. Natale, R. M. W. van Bijnen, A. Patscheider, D. Petter, M. J. Mark: Excitation Spectrum of a Trapped Dipolar Supersolid and Its Experimental Evidence . In: Physical Review Letters . tape 123 , no. 5 , August 1, 2019, p. 050402 , doi : 10.1103 / PhysRevLett.123.050402 ( aps.org [accessed November 1, 2019]).
  18. ↑ PW Anderson: Bose fluids above Tc: incompressible vortex fluids and 'supersolidity' . In: Phys. Rev. Lett. . 100, 2008, p. 215301.
  19. ↑ T.Matsubara, H. Matsuda: A lattice model of liquid helium . In: Prog. Theor. Phys . 16, 1956, pp. 569-582.