Dresden 2006 – scientific programme
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TT: Tiefe Temperaturen
TT 16: Solids At Low Temperature: Quantum Liquids, Bose-Einstein Condensates, Ultra-cold Atoms, ...
TT 16.7: Talk
Tuesday, March 28, 2006, 11:00–11:15, HSZ 105
Thermodynamics of strongly anisotropic roton system in superfluid 4He — •Valeriy Slipko1, Igor Adamenko1, Konstantin Nemchenko1, and Adrian Wyatt2 — 1Karazin Kharkov National University, Svobody Sq. 4, Kharkov 61077, Ukraine — 2School of Physics, University of Exeter, Exeter EX4 4QL, United Kingdom
Recently strongly anisotropic quasiparticle systems have been created in liquid 4He [1, 2]. The strong anisotropy means that the drift velocity can be close to the Landau critical velocity. By using the phonon-roton model, we have obtained analytical expressions for all thermodynamical functions up to the Landau critical velocity. It turns out that for strongly anisotropic quasiparticle systems of superfluid 4He, the temperature at which the contributions of phonons and rotons are comparable, decreases with increasing drift velocity. This creates a rather unusual situation; rotons can dominate in the whole temperature range. This is in contrast to isotropic quasiparticle systems, where the roton contribution to the thermodynamical functions, is negligible for temperatures less than 0.5 K. The reason for this unusual behavior of the roton thermodynamics is that, for velocities close to critical value, we cannot consider rotons as a classical gas which obeys Boltzmann statistics. Instead it must be considered by Bose statistics. The effective roton energy gap decreases when the drift velocity increases. This results in a large roton number density compared to the phonon number density, even at very low temperatures.
[1] Vovk R.V., Williams D.H. and Wyatt A.F.G. Phys. Rev. B68, 134508 (2003).
[2] Wyatt A.F.G. and Brown M. Physica B, 165&166, (1990).