Measurement of Vortex Motion in a Type-II Superconductor: A Novel Use of the Neutron Spin-Echo Technique

Forgan, E. M.; Kealey, P. G.; Johnson, S. T.; Pautrat, Alain; Simon, Ch.; Lee, Stephen; Aegerter, Christof M.; Cubitt, R.; Faragó, B.; Schleger, P.

doi:10.1103/physrevlett.85.3488

Cited by 19 publications

(15 citation statements)

References 8 publications

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“…This physics, which is based on the nonlinear response of the moving lattice, has previously been investigated for vortex lattices in superconductors. 37,38 Finally, also the current itself can distort the skyrmion lattice and lead to a reorientation of the lattice. By symmetry, this effect occurs, however, only to third order in the current density.…”

Section: Summary and Discussionmentioning

confidence: 99%

Current-induced rotational torques in the skyrmion lattice phase of chiral magnets

et al. 2011

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In chiral magnets without inversion symmetry, the magnetic structure can form a lattice of magnetic whirl lines, a two-dimensional skyrmion lattice, stabilized by spin-orbit interactions in a small range of temperatures and magnetic fields. The twist of the magnetization within this phase gives rise to an efficient coupling of macroscopic magnetic domains to spin currents. We analyze the resulting spin-transfer effects, and, in particular, focus on the current-induced rotation of the magnetic texture by an angle. Such a rotation can arise from macroscopic temperature gradients in the system as has recently been shown experimentally and theoretically. Here we investigate an alternative mechanism, where small distortions of the skyrmion lattice and the transfer of angular momentum to the underlying atomic lattice play the key role. We employ the Landau-Lifshitz-Gilbert equation and adapt the Thiele method to derive an effective equation of motion for the rotational degree of freedom. We discuss the dependence of the rotation angle on the orientation of the applied magnetic field and the distance to the phase transition.

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Section: Summary and Discussionmentioning

confidence: 99%

Current-induced rotational torques in the skyrmion lattice phase of chiral magnets

et al. 2011

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“…It is both understood and experimentally shown that the vortices, when submitted to an overcritical current I > I c and under steady state conditions, move in the bulk of the sample with a well defined average periodicity [8]. This motion is associated with a resistance R f f ≤ R n and an electrostatic field E = −V L ∧ ω (V L is the line velocity and ω the vortex field) [9].…”

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confidence: 99%

Voltage noise and surface current fluctuations in the superconducting surface sheath

Scola¹,

Pautrat²,

Goupil³

et al. 2005

Phys. Rev. B

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We report the first measurements of the voltage noise in the surface superconductivity state of a type-II superconductor. We present strong evidences that surface vortices generates surface current fluctuations whose magnitude can be modified by the pinning ability of the surface. Simple twostage mechanism governed by current conservation appears to describe the data. We conclude that large voltage fluctuations induced by surface vortices exist while the bulk is metallic. Furthermore, this experiment shows that sole surface current fluctuations can account for the noise observed even in the presence of vortices in the bulk.PACS numbers: 74.40.+k, 74.25.Op, 72.70.+m, 74.70.Ad Separating bulk and surface effects is an ubiquitous problem in condensed matter physics. For example, Flicker noise in semi-conductors [1] and 1/f like-noise in metals [2,3] can occur from either bulk or surface localized sources. Similarly, one can cite the long standing debate about surface versus bulk effects in driven nonlinear systems like charge density waves [4] or vortex lattice in superconductors [5,6]. Such debate extends to the origin of the fluctuations responsible for their electronic noise. In any case, the key question is how to determine the relevant sources of disorder. From a technological point of view, noise is a limiting factor for most of applications, and it is necessary to know its origin before expecting its minimization. It is also of theoretical interest to know if, when analyzing disordered systems, boundaries effects are of first importance or if they can be neglected compared to the pure bulk treatment of the problem. A similar question has lead to the proposition that bulk impurities play no major role in the broad band noise generation of charge density waves [7]. As a model system, the case of superconducting vortex lattices can be particularly instructing.The dynamics of a bulk vortex lattice has been heavily studied in the literature. It is both understood and experimentally shown that the vortices, when submitted to an overcritical current I > I c and under steady state conditions, move in the bulk of the sample with a well defined average periodicity [8]. This motion is associated with a resistance R f f ≤ R n and an electrostatic field E = −V L ∧ ω (V L is the line velocity and ω the vortex field) [9]. Experimentally, it was also shown that E can be separated into its mean E and its fluctuating part δE * [10]. The latter is the electric field noise. Combined with the V-I relation V = R f f (I − I c ), one can easily realize that this noise can be expressed as fluctuations in the bulk current (I − I c ), or as fluctuations in the resistance R f f . Most of the theories invoke bulk pinning centers through their interaction with the moving vortices, leading to vortex density fluctuations and to their associated δR * f f fluctuations [10]. Alternatively, noise may arise from over-critical current fluctuations δ(I − I c ) * , while R f f is constant [12]. For the simple reason of current conservation, δ(I...

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“…Details of the experimental setup and results are given in [6,10]. According to Josephson [11], when flux lines move, an electric field E is produced, which depends on their average velocity v L and the average induction B via v L = E/B.…”

Section: Neutron Spin Echo Measurementsmentioning

confidence: 99%

“…B is known and E may easily be measured by voltage contacts on the sample. Since the neutron energy change measured by NSE is directly proportional to v L [6], these measurements have allowed a direct check of the Josephson relationship. In addition, we have also demonstrated that one can detect a spread of flux line speeds, which macroscopic measurements of E would not Investigation of structures of moving flux lines reveal.…”

Section: Neutron Spin Echo Measurementsmentioning

confidence: 99%

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The microscopic investigation of structures of moving flux lines by neutron and muon techniques

2002

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We have used a variety of microscopic techniques to reveal the structure and motion of flux line arrangements, when the flux lines in low T c type II superconductors are caused to move by a transport current. Using small-angle neutron scattering by the flux line lattice (FLL), we are able to demonstrate directly the alignment by motion of the nearest-neighbor FLL direction. This tends to be parallel to the direction of flux line motion, as had been suspected from two-dimensional simulations. We also see the destruction of the ordered FLL by plastic flow and the bending of flux lines. Another technique that our collaboration has employed is the direct measurement of flux line motion, using the ultra-high-resolution spectroscopy of the neutron spin-echo technique to observe the energy change of neutrons diffracted by moving flux lines. The muon spin rotation (µSR) technique gives the distribution of values of magnetic field within the FLL. We have recently succeeded in performing µSR measurements while the FLL is moving. Such measurements give complementary information about the local speed and orientation of the FLL motion. We conclude by discussing the possible application of this technique to thin film superconductors.

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Measurement of Vortex Motion in a Type-II Superconductor: A Novel Use of the Neutron Spin-Echo Technique

Cited by 19 publications

References 8 publications

Current-induced rotational torques in the skyrmion lattice phase of chiral magnets

Current-induced rotational torques in the skyrmion lattice phase of chiral magnets

Voltage noise and surface current fluctuations in the superconducting surface sheath

The microscopic investigation of structures of moving flux lines by neutron and muon techniques

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