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Europhysics Letters (EPL)

Topological Transition of v -Vortex Core Matter in Superfluid 3 He- B

M.M. Salomaa, Григорий Ефимович Воловик

Published Nov 15, 1986• 10 citations
Publisher

Abstract

The core of the singly quantized nonaxisymmetric v -vortex in rotating 3 He- B is found to display novel topological structure: it is a bound pair of vortices with half-integer circulation . The topology for flaring-out of vorticity from the real space to the momentum space, due to boojums (nodes) on the Fermi surface, is discussed for both the axisymmetric and nonaxisymmetric v -vortices. This difference in topology may explain the physical nature of the observed first-order vortex-core transition in rotating superfluid 3 He- B .

DOI
10.1209/0295-5075/2/10/007

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•Apr 6, 2001•0 citations
The core of the singly quantized nonaxisymmetric v -vortex in rotating 3 He- B is found to display novel topological structure: it is a bound pair of vortices with half-integer circulation . The topology for flaring-out of vorticity from the real space to the momentum space, due to boojums (nodes) on the Fermi surface, is discussed for both the axisymmetric and nonaxisymmetric v -vortices. This difference in topology may explain the physical nature of the observed first-order vortex-core transition in rotating superfluid 3 He- B .
We present experimental proof that in rotating 3B^{3}\mathit{B}3B the vortex-core transition temperature TV{\mathit{T}}_{\mathit{V}}TV​ separates axisymmetric vortices above TV{\mathit{T}}_{\mathit{V}}TV​ from vortices with spontaneously broken axial symmetry below TV{\mathit{T}}_{\mathit{V}}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.
The authors consider the core structures of quantised vortex lines in Bose and Fermi superfluid systems. They emphasise the result that, within the core of a singly quantised vortex line in a Bose superfluid, there spontaneously appears a condensate of boson pairs in a relative d-wave state, instead of the normal fluid. Also, in the case of the singly quantised Abrikosov vortex line in a superconductor, instead of normal electrons there emerges a novel state of superconductivity, in which a condensate of bosons made of four fermions appears. In particular, they discuss these core structures as further examples for the flaring-out of the vortex singularity into higher dimensions, in analogy with the extended-space topology of the superfluid 3 He-B vortex core; they also relate this generic behaviour to the Laughlin state within the quantum Hall effect.
Triple-core structure of the double-core vortex in superfluid 3^33He-B
The order parameter of superfluid 3^33He involves nine complex components, and the multicomponent structure allows quantized vortices in superfluid 3^33He to have complicated cores. One of the vortices found in the B phase is the double-core vortex, which has been often described as a pair of two half-quantum vortices (HQVs) connected by a domain wall. Our numerical calculations of the core structure suggest an alternative representation of the vortex as a combination of three vortices, one in each component of the spin-triplet superfluid. Based on the results we present a qualitative analytical model for the triple-core structure of the double-core vortex. Additionally we numerically calculate the structure of a double-core vortex stretched between pinning sites, and show that the HQV picture becomes more applicable when separation between subcores becomes large.
Triple-Core Structure of the Double-Core Vortex in Superfluid 3^33He-B
Abstract The order parameter of superfluid 3^33 3 He involves nine complex components, and the multicomponent structure allows quantized vortices in superfluid 3^33 3 He to have complicated cores. One of the vortices found in the B phase is the double-core vortex, which has been often described as a pair of two half-quantum vortices (HQVs) connected by a domain wall. Our numerical calculations of the core structure suggest an alternative representation of the vortex as a combination of three vortices, one in each component of the spin-triplet superfluid. Based on the results we present a qualitative analytical model for the triple-core structure of the double-core vortex. Additionally we numerically calculate the structure of a double-core vortex stretched between pinning sites, and show that the HQV picture becomes more applicable when separation between subcores becomes large.
This doctoral thesis consists of experimental studies on rotating superfluid helium-3 at millikelvin temperatures. Superfluid 3He provides an example of ordered systems where quantum phenomena are visible on a macroscopic scale. The order parameter is described by a 3x3 complex matrix leading to different superfluid phases with different properties. The A and B phases support topologically different kinds of defects, most notably vortex lines. Vortex lines are most easily created and studied in uniform rotation. Because of quantum nature, the circulation around the vortices is quantized in units of κ0 = h/2m3.\n\nIn superfluid 3He nuclear magnetic resonance (NMR) provides a means to distinguish between different types of vortices and count them one by one. During the course of this work the sensitivity of the NMR spectrometer was improved by an order of magnitude, which enabled the direct measurement of the circulation of a vortex in the A phase that carries two circulation quanta (2κ0). Up to now the circulation of the known quantized vortex types in other quantum fluids, which include superfluid 4He, superconductors, and Bose-Einstein -condensates, has been singly quantized.\n\nOther NMR experiments reported in the thesis are: (1) The first qualitative measurements of vortex annihilation in the A and B phases of 3He. These measurements tell the lowest rotation velocity that stabilizes an array of vortex lines with a given number of vortices, and how it depends on the type of the defect. (2) Studies of vortex arrays with both singly and doubly quantized A phase vortex lines coexisting in the experimental container. 3He-A provides a unique system in which this kind of arrangement can be done. (3) In order to improve the vortex detection sensitivity in the B phase even further, the response of different nonlinear spin precession modes to superfluid-normal fluid counterflow was studied. A new mode, where the orbital angular momentum is oriented transverse to the external magnetic field, was found.