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[1]Dynamics of vortices and interfaces in superfluid 3He; A.P. Finne, V.B. Eltsov, R. Hän­ni­nen, N.B. Kop­nin, J. Kopu, M. Krusius, M. Tsubota, and G.E. Volovik, Rep. Prog. Phys. 69, 3157-3230 (2006).

[2]Turbulent dynamics in rotating helium superfluids; V.B. Eltsov, R. de Graaf, R. Hän­ninen, M. Krusius, R.E. Solntsev, V.S. L’vov, A.I. Golov, and P.M. Walmsley, Prog. Low Temp. Phys. Vol. XVI, ed. M. Tsubota (Elsevier Publ., Amsterdam, 2008) [preprint arXiv:0803.3225].

[3]Vortex multiplication in applied flow: a precursor to superfluid turbulence;  A.P. Finne, V.B. Elt­sov, G. Eska, R. Hänninen, J. Kopu,  M. Krusius, E.V. Thuneberg, and M. Tsu­bota, Phys. Rev. Lett. 96, 085301 (2006).

[4]Twisted vortex state; V.B. Eltsov, A.P. Finne, R. Hänninen, J. Kopu, M. Krusius, M. Tsubota, and E.V. Thuneberg, Phys. Rev. Lett. 96, 215302 (2006).

[5]Quantum turbulence in a propagating superfluid vortex front; V.B. Eltsov, A.I. Golov, R. de Graaf, R. Hän­ninen, M. Krusius, V.S. L’vov, and R.E. Solntsev, Phys. Rev. Lett. 99, 265301 (2007).


Harry Alles, Heikki Junes, Matti Manninen, and Igor Todoshchenko


Helium crystals are quantum crystals which exhibit several exotic properties. For instance, at low enough temperatures they can grow and melt so easily that a melting-freezing wave, a crystallization wave, can propagate along their surface. At the same time they represent an ideal model system to study general properties of the crystal surface, such as an equilibrium crystal shape, faceting-roughening transitions, growth kinetics, etc. Furthermore, the two stable helium isotopes, 3He and 4He, have different quantum statistics, that is bosonic and fermionic, correspondingly, resulting in quite different properties of the liquid-solid interfaces as well as of the bulk phases. In the case of 3He, due to nuclear spin, also the effect of the magnetic field could be investigated.

Recently the interest to the studies of the properties of solid helium has been lifted by the experimental results of Kim and Chan from Pennsylvania State University who reported on the evidence of superfluidity of solid 4He. They studied the rotational inertia of a torsional oscillator filled with solid 4He and discovered about 1% decoupling of mass below 200 mK. This decoupling, named as “non-classical rotational inertia”, has by now been confirmed by several other experimental groups. In later experiments that the size of decoupling is observed to be greatly influenced by crystalline defects within the solid 4He, as well as by the amount of 3He impurities. However, despite of extensive study it is not clear if this interesting phenomenon is really related to the supersolid state of the matter.

The INTERFACE group has been studying the surface of both 4He and 3He crystals by optical means. The shape of the crystals was imaged by a Fabry-Pérot interferometer built inside the nuclear demagnetization cryostat. One of the most important results obtained with the interferometric setup was that altogether 11 different types of facets (flat surface parts) have been observed on 3He crystals at 0.55 mK which could be looked as a proof of the devil’s staircase phenomenon which was predicted by Lev Landau in 1950s.

Annual Report 2007

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