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Ions and the Landau critical velocity in He II.

Research output: Contribution to journalJournal article


<mark>Journal publication date</mark>09/1995
<mark>Journal</mark>Zeitschrift für Physik B Condensed Matter
Issue number3
Number of pages6
Pages (from-to)429-434
<mark>Original language</mark>English


Investigations of the motion of conventional negative ions (electron bubbles) in He II under pressures above 11 bar have provided the only means of measuring the Landau critical velocity for roton creation, VL, and for studying supercritical dissipation at higher velocities. Earlier work on roton creation is reviewed and it is pointed out that there is still no generally agreed explanation of the fact that the rotons seem to be emitted from the moving ion in pairs; nor is it known why the matrix element characterising the pair emission process should decrease rapidly with pressure. The possibility of studying these phenomena through use either of the "fast ion" (whose nature remains unknown), or of selected ions from the large variety of species that can be injected into He II by the recently developed technique of laser ablation, is discussed.

Bibliographic note

Proceedings of the 128th WE-Heraeus Seminar on Ions and Atoms in Superfluid Helium, Heidelberg Germany, 16-19 May 1994