Gap anisotropy, vortex cluster, and nucleation of vortices in rotating 3He-B

Kondo, Yasushi; Korhonen, J. S.; Parts, Ü.; Krusius, M.; Lounasmaa, O. V.; Gongadze, A. D.

doi:10.1016/0921-4526(92)90183-s

Cited by 24 publications

(3 citation statements)

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“…The bundle is separated from the wall by an annular vortex-free layer which carries counterflow of the normal and superfluid components at the velocity v = Qr -Q V R 2 /r. This distribution of vortices and their numbers can be inferred from the absorption spectrum of continuouswave NMR [2]. £?-phase vortices were counted with a resolution of « 0.01 rad/s = 10 vortices.…”

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Vortex layer on the interface between theAandBphases in superfluidHe3

et al. 1993

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Using NMR techniques we monitor the structure and number of vortices in a cylindrical container, rotating at constant angular velocity Q, before and after the passage of the A-B interface. The initial A phase contains the equilibrium number of vortices. The final B phase is found to have a deficit of vortices which depends nonmonotonically on the measured time £AB of the A -• B transition. We argue that a vortex layer is formed in front of the moving A-B interface. The measured vortex deficit can be understood by analyzing the stability of the layer.PACS numbers: 67.57.Fg, 67.57.Np The superfluid phases of 3 He support a rich variety of topological objects [1], The interface between the A and B phases offers a unique possibility to study the continuity of linear objects through a first order phase boundary. Consider the quantized vortices shown in Fig. 1. The prevailing vortex in the A phase is continuous, which means that the vorticity is distributed over a large crosssectional area (shaded tubes). In the B phase, the vortices are singular; i.e., the vorticity is concentrated into a core of the size of the superfluid coherence length (« 10 nm), which is « 10~3 of the length characterizing the core of a continuous vortex. We may ask what happens when the £?-phase volume grows at the expense of the A phase: Are A-phase vortices compressed and transformed to B-phase vortices or are they pushed aside in front of the interface? We find experimentally that both processes take place. Part of the A-phase vortices form a layer, which is pushed in front of the moving inter-FIG. 1. The continuous ^4-phase vortex (shaded tube on the right) and its two possible fates when the B phase expands to the right: (a) The ^4-phase vortex is pushed in front of the A-B interface (shaded surface) and eventually a layer of vortices will accumulate to cover the interface, (b) The continuous vortex is compressed so that it can penetrate through the interface and forms two singular S-phase vortices (lines), as required by the conservation of circulation. The continuous vortex terminates in a singular point on the wall, which may lower the energy barrier for the alternative (b) [1].face. The stability of the vortex layer seems to control the fraction of the vortices that leaks through the A-B interface.Experiment-Our NMR cell is a cylinder of radius R = 3.5 mm and height L = 7 mm. It is connected via an orifice of 1 mm in diameter to the rest of the 3 He volume, which contains a Pt thermometer and a sintered heat exchanger. The vortices are stabilized by continuous rotation around the axis of the cylinder. Measurements were performed at 29.3 bars pressure in magnetic fields of 14.2 or 28.4 mT. Initially the 3 He sample in the NMR cell was prepared to contain the equilibrium number of vortices in the A phase. This was done by accelerating the cryostat from rest to high speed and then decelerating to the desired angular velocity Q. The A-B interface was next allowed to pass through the cell at constant fl, and subsequently the number of vor...

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“…Here u is the interface velocity, B the dissipative friction parameter, B = 2npp s D/p n [(p s K -.D f ) 2 4-D 2 ) [5], and V C Q = 2f c /p s K a bare critical velocity. Assuming for B the measured bulk value [7], we can extract v c o by fitting (1) to the data in Fig.…”

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Vortex layer on the interface between theAandBphases in superfluidHe3

et al. 1993

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“…NMR in an axial magnetic field (H(1Q). The NMR line shape depends upon the B-phase order parameter texture and thereby provides a measure of the azimuthal macroscopic counterflow U [5]. During acceleration the B-phase anisotropy axis is deflected away from the direction of H by the increasing counterflow U.…”

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Single-Vortex Nucleation in Rotating Superfluid ³ He-B

Parts¹,

Ruutu²,

Koivuniemi³

et al. 1995

Europhys. Lett.

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Nucleation of vortices in units of one quantum has been observed with C.W. NMR in a rotating cylinder filled with 3He-B. During acceleration a new vortex is created each time the counterflow velocity at the perimeter reaches a critical value v,(T, p ) . The measured v, resembles the calculated velocity v,b (T, p ) of the bulk superflow instability, but is smaller by a factor with power law dependence on the superfluid coherence length. This indicates that a nucleation event takes place whenever the flow exceeds v,b locally at the nucleation site and the nucleation barrier vanishes.

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