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A direct interrogation of superfluidity on molecular scales A. V. Benderskii,a)

Summary: A direct interrogation of superfluidity on molecular scales
A. V. Benderskii,a)
J. Eloranta, R. Zadoyan,b)
and V. A. Apkarianc)
Department of Chemistry, University of California, Irvine, California 92697-2025
Received 5 February 2002; accepted 25 April 2002
Time-resolved, pump­probe measurements are used to directly interrogate dissipative fluid
dynamics in bulk He-II, on molecular scales, as a function of temperature and pressure. The Rydberg
transitions of the triplet He2* excimers, which solvate in bubble states in liquid helium, are used as
nanoscale transducers to initiate and to directly monitor the motion of the fluid in the form of
damped oscillations of a 13 Ĺ spherical bubble. The oscillations are damped out after one period,
with a temperature-dependent period that directly tracks the normal fraction. As such, the bubble
oscillator acts as a nanoviscosimeter. Through simulations of the observed signals, it is established
that the coherent response of the bath obeys hydrodynamic equations of motion of a continuum
subject to two-fluid flow. Dissipation occurs through two distinct channels: a Radiation of sound
in the farfield, driven by the acceleration of volume in the compressible fluid; b
temperature-dependent drag in the near-field. The drag can be considered to be strictly viscous in
origin, or due to ballistic scattering of rotons from the bubble edge. The experiments do not
distinguish between these two microscopic models. With this caveat in mind, it can be concluded
that for these breathing modes of bubble states, the macroscopic concepts of superfluidity scale


Source: Apkarian, V. Ara - Department of Chemistry, University of California, Irvine


Collections: Chemistry