Creation of high-energy phonons by four-phonon processes in anisotropic phonon systems of He II

• Published in: Физика низких температур
• Date: 2007
• Main Authors: Adamenko, I.N., Kitsenko, Yu.A., Nemchenko, K.E., Slipko, V.A., Wyatt, A.F.G.
• Format: Article
• Language: English
• Published: Фізико-технічний інститут низьких температур ім. Б.І. Вєркіна НАН України 2007
• Subjects: Квантовые жидкости и квантовые кpисталлы
• Online Access: https://nasplib.isofts.kiev.ua/handle/123456789/127809
• Journal Title: Digital Library of Periodicals of National Academy of Sciences of Ukraine
• Cite this: Creation of high-energy phonons by four-phonon processes in anisotropic phonon systems of He II / I.N. Adamenko, Yu.A. Kitsenko, K.E. Nemchenko, V.A. Slipko, A.F.G. Wyatt // Физика низких температур. — 2007. — Т. 33, № 5. — С. 523-537. — Бібліогр.: 22 назв. — англ.

The problem of the creation of high-energy phonons (h-phonons) by a pulse of low-energy phonons
 (l-phonons) moving from a heater to a detector in superfluid helium, is solved. The rate of h-phonon creation
 is obtained and it is shown that created h-phonons occupy a much smaller solid angle in momentum space,
 than the l-phonons. An analytical expression for the creation rate of h-phonon, along the symmetry axis of a
 pulse, are derived. It allows us to get useful approximate analytical expressions for the creation rate of
 h-phonons. The time dependences of the parameters which describe the l-phonon pulse are obtained. This
 shows that half of the initial energy of l-phonon pulse can be transferred into h-phonons. The results of the
 calculations are compared with experimental data and we show that this theory explains a number of experimental
 results. The value of the momentum, which separates the l- and h-phonon subsystems, is found.