Ultrasonic investigation of 3He-A vortices in low magnetic fields

K. Torizuka, J.P. Pekola, A. J. Manninen

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We report ultrasonic measurements on rotating 3He-A at 26.7 bar pressure and at magnetic fields below 12.0 mT. We observed two distinct types of vortices: the attenuation of zero sound by vortices which were created at small fields is higher than the attenuation by vortices created at high fields. The first order transition between the two vortex states was observed at Hc∼HD ({all equal to}3 mT). The low field structure can be identified with type-I vortices proposed by Fujita et al. and the high field one with that of Seppälä and Volovik and initially discovered in NMR experiments. The structural change may be viewed as a topological transition, because the d̂-vector distribution is different for the dipole-locked vortices in low fields from that for the dipole-unlocked vortices in high fields. In addition, a continuous change between coreless vortices and vortices with a well-defined core was observed at low enough fields H′ ≪ Hc. The vortices in 3He-A can, therefore, be characterized by three magnetic fields: H′, Hc, and Hcl. The last is the catastrophe field at which the dipole-locked vortices become unstable.

Original languageEnglish
Pages (from-to)244-261
Number of pages18
JournalPhysica B: Physics of Condensed Matter
Issue number1-4
Publication statusPublished - 2 May 1992
MoE publication typeA1 Journal article-refereed


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