Direct observation of the nonaxisymmetric vortex in superfluidB3

Abstract

We present experimental proof that in rotating 3 He-Z? the vortex-core transition temperature 7V separates axisymmetric vortices above TV from vortices with spontaneously broken axial symmetry below TV. The nonaxisymmetry is observed in the presence of coherent spin precession as a new soft Goldstone mode, manifested as oscillations and spiral twisting of the core anisotropy axis. These are driven by the precessing spin via spin-orbit coupling and lead to magnetic relaxation from viscous losses, which depend on vortex pinning.PACS numbers: 67.50.FiThe quantized vortices of superfluid He-Z? were discovered in 1981: An abrupt change in NMR frequency shifts at a critical phase-transition line Ty(p) in the temperature-(T-) pressure (p) plane was interpreted to represent a change in the structure of the vortex core. l Theoretical investigations 2,3 in the Ginzburg-Landau regime close to T c revealed two types of vortices with the same number of circulation quanta but with different internal symmetries of their cores. At high pressure the most stable vortex is the axisymmetric V\ vortex 2 with broken parity and with 3 He-A superfluid inside a core with a diameter of several coherence lengths £o~13 nm. At low pressure the rotational symmetry is broken, resulting in the V2 vortex with a nonaxisymmetric double core, 3 which may be considered a bound state of two half-quantum vortices (see insets in Fig. 1). This is now regarded as being consistent with existing experimental information. 4 Here we present the first direct experimental evidence that the phase transition, indeed, separates an axisymmetric V\ vortex at high temperatures from an asymmetric V2 vortex at low temperatures. The results were obtained by making use of the homogeneously precessing magnetic domain 5 (HPD), an NMR mode of 3 He-Z? which has proven to be more sensitive to the core structure than conventional NMR. In the HPD mode all spins within the resonance domain precess uniformly at a tipping angle of roughly 104°. Several relaxation mechanisms contribute to losses in this mode; however, here we are only concerned with the absorption caused by vortices. 6 This additional absorption Py is proportional to the total length of vortices within the precessing domain and increases discontinuously by a factor of 3 at Tyip) during cooling. 7 It also turns out that the HPD absorption of a vortex array with a constant number Ny of V2 vortices depends on whether or not the rotation velocity ft is maintained constant: If ft changes with time then an increase APf in the absorption level Pvi is observed. We explain this unique feature in terms of the dipolar coupling between the homogeneously precessing total spin magnetization and the orbital inhomogeneity in the vortex-core region. The HPD absorption from V2 vortices is dominated by a soft Goldstone mode, associated with the viscous dynamics of the in-plane orbital anisotropy vector b of the asymmetric vortex core. The Goldstone mode is manifested by (i) rapid viscous oscillatory motion and by (ii) slow rotationa...

Disappearance of Meissner Effect and Specific Heat Jump in a Multiband Superconductor, Ba0.2K0.8Fe2As2

“…This inhibits ejection of the vortex and the Meissner effect. A similar texture structure and its dynamics have also been reported in other multicomponent systems such as the superfluid 3 He [25][26][27][28][29]. We can expect a similar situation to occur in Ba 0.2 K 0.8 Fe 2 As 2 .…”

Energetically stable singular vortex cores in an atomic spin-1 Bose-Einstein condensate

“…[57,58] and experimentally observed in Ref. [59]. The 3 He A-phase core was explained to consist of two half-quantum vortices.…”

“…The splitting can be understood from the nematic symmetry properties of the polar order parameter. A stable nonaxisymmetric singular vortex with a nonzero superfluid density at the core has been theoretically predicted [57,58] and experimentally observed [59] in superfluid liquid 3 He. Here we analyze the energetic stability of the singular vortices and explain the structures of their cores by numerical simulations in the framework of mean-field theory.…”

Calculation of Leggett–Takagi Relaxation in Vortices of Superfluid $$^{3}$$ 3 He-B

“…The measured quantity is the absorbed energy. Based on the relative jump of the observables at the transition between the vortex types, the latter method is more sensitive to the vortex structure than the former [5].…”

“…For larger tipping one gets the Brinkman-Smith mode [4], where the texture is erased. At angles exceeding the Leggett angle 104 • this forms the homogeneously precessing domain (HPD) [5]. Here the spins within the domain precess uniformly even in a nonuniform magnetic field.…”