Experiments with negative ions in3He superfluids

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, _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 _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 yields _A (T)=1.32 _BCS (T) for the maximal A phase gap atP=29.3 bar, and _B (T)=1.12 _BCS (T) for the B phase gap at 4.8 bar. In the normal Fermi liquid a shallow minimum of ion mobility was detected aroundT2T _c =5 mK.