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We start with Landau criterium for superfluidity and consider the excitation spectrumSpectrumexcitation spectrum in superfluid He–4He-4 consisting of phonon and roton branches. We introduce the two-fluid description of liquid heliumHeliumliquid and discuss the classical experiments of Kapitza–Allen–Jones et al., the first and second soundSoundsecond sound modes in He, as well as the temperature dependence of the normal densityDensitynormal densityNormal density and second soundSoundsecond sound velocity in it. We analyze the formation of the Feynman–Onsager vortex latticesLatticevortex latticeVortex lattice in rotational helium and Bose condensatesBose condensate of quantum gasesGasquantum gasQuantum gas and determine the first and second critical rotation frequencies.

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Lecture 4. Superfluid Helium. Sounds and Vortices

  • 章节

  • 发表日期：

    2026年

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  • Maxim Kagan

摘要

We start with Landau criterium for superfluidity and consider the excitation spectrumSpectrumexcitation spectrum in superfluid He–4He-4 consisting of phonon and roton branches. We introduce the two-fluid description of liquid heliumHeliumliquid and discuss the classical experiments of Kapitza–Allen–Jones et al., the first and second soundSoundsecond sound modes in He, as well as the temperature dependence of the normal densityDensitynormal densityNormal density and second soundSoundsecond sound velocity in it. We analyze the formation of the Feynman–Onsager vortex latticesLatticevortex latticeVortex lattice in rotational helium and Bose condensatesBose condensate of quantum gasesGasquantum gasQuantum gas and determine the first and second critical rotation frequencies.