Spatial distribution of vortices and anisotropy of mutual friction in rotating He II

Mathieu, P.; Plaçais, Bernard; Simon, Y.

doi:10.1103/physrevb.29.2489

Cited by 31 publications

(31 citation statements)

References 7 publications

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“…1(a)], the boundary condition (3) entails two perturbed layers, where equilibrium supercurrents are nothing but Meissner-like diamagnetic currents. We have shown [17] that a similar elTect exists in a rotating cavity in Hell, in agreement with experiment (see Fig. 1 in Ref.…”

supporting

confidence: 87%

Critical-current fluctuations and flux-flow noise in type-II superconductors

Plaçais¹,

Mathieu²,

Simon³

1993

Phys. Rev. Lett.

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By relying on a recent theory of transport in the mixed state and a related model of pinning in soft materials, the instantaneous critical current is introduced as a well-defined part I\ of the total constant current. This nondissipative and time-dependent I\ is assumed to be randomly distributed near the sample surface, and is described as a 2D turbulent homogeneous flow. Auto-and cross-correlation functions of both voltage and magnetic field noises are predicted and are in full agreement with experiments.PACS numbers: 74.60.Ge, 74.60Jg Flux-flow noise has been extensively studied, particularly during the 1960's and 1970's [1-6]. The spectrum and amplitude of the noise voltage dV(t), typically 10 ~^-10 "'' V/(Hz) ^/^ in the 0-10 kHz bandwidth, were regarded as significant parameters revealing the more or less irregular motion of vortex lines (VL) in the presence of pinning. The reader is referred to the excellent critical review by Clem [7]. In view of the experimental difficulties and the increasing intricacy of interpretations, this scope has been practically discarded since about 1980.It should be noted that soft samples were used, classically shaped as foils or strips perpendicular to the applied magnetic field. Low to moderate critical currents /^ are required to avoid spurious sources of noise due to excessive dissipation, such as flicker noise [7]. Therefore, at working temperatures (4.2 K [1,2,5] or close to the X point [6]), the authors had to operate at the onset of the /-K curve; in this region, where flux flow is essentially inhomogeneous along the sample [8], measurements yield unreliable results.Recently [9], we have reconsidered the problem of noise, both theoretically and experimentally. We have performed a series of experiments in superfluid helium in order to widely explore the flux-flow regime. Voltage noise, magnetic field noise around the sample, and thermal Joule noise [10] were investigated, as well as their cross correlations. By relying on a phenomenological theory of vortex motion, recently published by two of us, Mathieu and Simon (MS) [11], we were able to work out a consistent theory of noise, the principle of which is brought forward in this Letter.Roughly speaking, two mechanisms have been advanced to account for the voltage noise quantitatively. In their pioneering work, van Ooijen and van Gurp [1] assumed that flux bundles nucleated randomly at one edge and moved rigidly across the sample with constant velocity VL. This process gives rise to a time sequence of statistically independent pulses, the cutoff' frequency of the noise spectrum being related to the time of flight of bundles. This analogy with the electronic "shot noise" was attractive, but more and more adjustable parameters were introduced to fit the data; besides the flux bundle size ipb, others include the fraction of pinned vortices [2], or a distribution of subpulse times [6]. Somewhat artificially, ipb is found to be a rapidly decreasing function of current, falling off* below the flux quantum <^o [2,6]. Moreov...

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supporting

confidence: 87%

Critical-current fluctuations and flux-flow noise in type-II superconductors

Plaçais¹,

Mathieu²,

Simon³

1993

Phys. Rev. Lett.

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“…The most striking result, which differs from the general view and from the results assumed in Ref. [5], is that far from boundaries the vortices may tend to align not along the rotation axis but along the symmetry axis of the rotating cylinder. This is especially true for a single vortex under high rotation and for an array with a large number of vortices.…”

Section: Introductioncontrasting

confidence: 79%

Rotating Inclined Cylinder and the Effect of the Tilt Angle on Vortices

Hänninen¹

2009

J Low Temp Phys

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We study numerically some possible vortex configurations in a rotating cylinder that is tilted with respect to the rotation axis and where different numbers of vortices can be present at given rotation velocity. In a long cylinder at small tilt angles the vortices tend to align along the cylinder axis and not along the rotation axis. We also show that the axial flow along the cylinder axis, caused by the tilt, will result in the Ostermeier-Glaberson instability above some critical tilt angle. When the vortices become unstable the final state often appears to be a dynamical steady state, which may contain turbulent regions where new vortices are constantly created. These new vortices push other vortices in regions with laminar flow towards the top and bottom ends of the cylinder where they finally annihilate. Experimentally the inclined cylinder could be a convenient environment to create long lasting turbulence with a polarization which can be adjusted with the tilt angle.

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“…Since the transition is first order, it should occur above the thermodynamic transition field E c . This can be seen by the fact that the second term in the right hand side of Equation (25) does not produce any vertical force on the lines and do not contribute to their expulsion of the cell by the up surface (though they will produce strong horizontal forces preventing their reentrance and pushing them towards the lateral cell boundaries). The transition occurs actually at the « superheated » critical field E sh at which the vertical electric forces on the lines compensate the elastic forces generated by the helix.…”

Section: Unwinding Critical Fieldsmentioning

confidence: 99%

Dechiralisation lines–induced unwinding in confined SmC* liquid crystals

Mettout

Logbo²,

Vasseur

et al. 2016

Liquid Crystals

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Equilibrium and dynamic behaviours of dechiralisation lines occurring below SmC* cell boundaries in planar geometry constitute a polemic topic for several decades. We report new observations in the SmC* phase of the strongly polarized liquid crystal CFL08. They are compared with vortex motions in superfluids and type-II superconductors, and we propose a simple heuristic model attempting to explain the intriguing mismatch between bulk helix pitch and inter-lines distance. It results from opposite effects of the helix pitch and surface lines charge value on the equilibrium lines distance. The model assumes that the lines electric interactions dominate the cell equilibrium state. In particular the unwinding transition of the bulk helix is provoked by fieldinduced displacements of the lines lattices. It permits to relate the lines density and critical fields to intrinsic energy parameters, and to explain the pitch/distance mismatch, together with its almost constant value across the transition. We foresee the helix pitch and unwinding field variations vs. sample width.

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Spatial distribution of vortices and anisotropy of mutual friction in rotating He II

Cited by 31 publications

References 7 publications

Critical-current fluctuations and flux-flow noise in type-II superconductors

Critical-current fluctuations and flux-flow noise in type-II superconductors

Rotating Inclined Cylinder and the Effect of the Tilt Angle on Vortices

Dechiralisation lines–induced unwinding in confined SmC* liquid crystals

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