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High Resolution Phonon-assisted Quasi-resonance Fluorescence Spectroscopy
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Roton-phonon interactions in superfluid 4He.

B Fåk1, T Keller, M E Zhitomirsky

  • 1SPSMS, UMR-E CEA/UJF-Grenoble 1, INAC, F-38054 Grenoble, France.

Physical Review Letters
|October 30, 2012
PubMed
Summary

High-resolution neutron spin-echo measurements reveal distinct temperature dependencies between roton energy and inverse lifetime in superfluid helium-4. This suggests a repulsive roton-phonon interaction, influenced by three- and four-particle processes.

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Area of Science:

  • Condensed Matter Physics
  • Quantum Fluids
  • Superfluid Helium-4

Background:

  • Superfluid helium-4 exhibits unique quantum phenomena, including rotons and phonons.
  • Understanding quasiparticle interactions is crucial for characterizing superfluid dynamics.

Purpose of the Study:

  • To investigate the temperature dependence of roton energy and lifetime in superfluid 4He.
  • To elucidate the underlying mechanisms governing roton-phonon interactions.

Main Methods:

  • High-resolution neutron resonance spin-echo (NRSE) spectroscopy.
  • Diagrammatic perturbation theory for analyzing particle interactions.

Main Results:

  • Roton energy and inverse lifetime display different temperature dependencies.
  • Three- and four-particle processes involving phonons significantly influence roton dynamics.
  • Broken gauge symmetry in the Bose-condensate enables three-particle roton-phonon interactions.

Conclusions:

  • The observed distinct temperature dependencies indicate a net repulsive interaction between rotons and phonons at low temperatures.
  • The findings provide insights into the complex interplay of excitations in superfluid systems.