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Physical Review A

Low-Temperature Mobility of Trapped Ions in Rotating He II

Alexander L. Fetter, Ienari Iguchi

Published Nov 1, 1970• 45 citations
Publisher

Abstract

A classical vortex with a movable impurity in its core is used to study the interaction of vortex waves with a trapped ion in rotating He II. The reflection probability is evaluated in the long- and short-wavelength limits. An approximate interpolation formula allows a calculation of the low-temperature mobility of an ion along the vortex axis.

DOI
10.1103/physreva.2.2067

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Unknown eBooks•Oct 1, 1988•0 citations

Mobility of Negative Ions along Superfluid Vortices

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The mobility of negative ions along superfluid vortices is calculated on the basis of an appropriate model. The finite trapping force is taken into account, giving a resonance peak in the reflection coefficient of the vortex waves. The Doppler effect due to the ion motion is also taken into consideration. The numerical result is compared with experiment.

Progress of Theoretical Physics•Jun 1, 1971•6 citations
A classical vortex with a movable impurity in its core is used to study the interaction of vortex waves with a trapped ion in rotating He II. The reflection probability is evaluated in the long- and short-wavelength limits. An approximate interpolation formula allows a calculation of the low-temperature mobility of an ion along the vortex axis.
The mobility of negative ions trapped on linear vortices in rotating superfluid helium has been measured by a time-of-flight technique in the temperature range $0.8\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}<T<1.6\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}$. Measurements could not be extended below 0.8\ifmmode^\circ\else\textdegree\fi{}K because, contrary to the present theory, the ion escape rate became too large. No evidence of direct trapping of positive ions by vortex lines was observed down to 0.4\ifmmode^\circ\else\textdegree\fi{}K. The trapped-ion mobility is interpreted in terms of scattering of the ion by thermal distributions of quantized vortex waves and rotons localized about the vortex axis.
The lifetimes of both positive and negative ions trapped on quantized vortex lines in rotating 3He^{3}\mathrm{He}3He-4He^{4}\mathrm{He}4He mixtures have been measured at temperatures down to 0.1 K. Evidence is found that the 3He^{3}\mathrm{He}3He condenses at the vortex core, and possibly at the surface of the electron bubble.
The interaction between negative ions and 3 He superfluids was studied by using a time-of-flight spectrometer having a 10−3 relative resolution. The ions guided through a sample of rotating3He-A were found to be focused into the cores of the vortices present in this rotating superfluid. Two different types, with different core structures and presumably different numbers of circulation quanta associated with them, were found. The ion mobility along the vortex cores, μ c , observed in the absence of external magnetic field, can be explained by the mobility anisotropy of the A phase, which indicates that the vortices are continuous, i.e., consist of the A phase even in the core. In finite magnetic fields, a qualitatively similar continuous vortex structure was found, a result compatible with the earlier nuclear magnetic resonance (NMR) experiments, but also a new vortex type with an anomalously high μ c was seen when the vortex sample was prepared “adiabatically.” The observed strong ion focusing indicates broken w-symmetry in the core textures. This is in contradiction with the earlier numerical calculations on the optimal continuous vortex texture. Experiments to observe trapping of ions into the vortex cores were performed both in A and B phases. No trapping could be detected. Mobility measurements in stationary liquid were extended down toT=0.3T c . Comparison with the calculated transport coefficients yieldsΔ A (T)=1.32Δ BCS (T) for the maximal A phase gap atP=29.3 bar, andΔ B (T)=1.12Δ BCS (T) for the B phase gap at 4.8 bar. In the normal Fermi liquid a shallow minimum of ion mobility was detected aroundT≃2T c =5 mK.