Closer look at the low-frequency dynamics of vortex matter using scanning susceptibility microscopy

Raes, Bart; Silva, Clécio C. de Souza; Silhanek, Alejandro; Cabral, Leonardo R.E.; Moshchalkov, Victor; Vondel, J. Van de

doi:10.1103/physrevb.90.134508

Cited by 11 publications

(17 citation statements)

References 42 publications

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“…However, in weak pinning superconductors, these states are characterized by a dilute distribution of topological defects that can be healed by e.g. thermal fluctuations, gentle ac shaking or a combination of both 43 . It is also noteworthy that, in an actual experiment, the vortex configuration observed at the sample surface might differ from that found in the bulk due to vortex bending, which is neglected in our 2D approach.…”

Section: Discussionmentioning

confidence: 99%

Conformal Vortex Crystals

Menezes

Silva

2017

Sci Rep

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We investigate theoretically globally nonuniform configurations of quantized-flux vortices in clean superconductors trapped by an external force field that induces a nonuniform vortex density profile. Using an extensive series of numerical simulations, we demonstrate that, for suitable choices of the force field, and bellow a certain transition temperature, the vortex system self-organizes into highly inhomogeneous conformal crystals in a way as to minimize the total energy. These nonuniform structures are topologically ordered and can be mathematically mapped into a triangular Abrikosov lattice via a conformal transformation. Above the crystallization temperature, the conformal vortex crystal becomes unstable and gives place to a nonuniform polycrystalline structure. We propose a simple method to engineer the potential energy profile necessary for the observation of conformal crystals of vortices, which can also be applied to other 2D particle systems, and suggest possible experiments in which conformal or quasi-conformal vortex crystals could be observed in bulk superconductors and in thin films.

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Section: Discussionmentioning

confidence: 99%

Conformal Vortex Crystals

Menezes

Silva

2017

Sci Rep

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“…3,8,9 In contrast to standard susceptibility measurements, in SSM the periodic change in flux due to vortex motion and screening currents is measured locally by scanning a submicron-sized Hall probe over the surface, thereby revealing the microscopic vortex response. Moreover, the screening current response imaged close to the border, also probed in classical macroscopic ac-susceptibility experiments, can be cross-correlated with the present vortex physics and the theoretical models describing them.…”

Section: And References Therein)mentioning

confidence: 99%

“…The details of the technique can be found in Ref. 3. In summary, the superconducting sample is surrounded by a copper coil, which is mounted coaxially in the bore of the superconducting magnet and generates an ac field h(t) = h ac cos ωt parallel to the dc field.…”

Section: B Scanning Ac Susceptibility Imagesmentioning

confidence: 99%

“…1, we present the profiles of the local magnetic permeability b ac (x)/h ac of a superconducting strip, which is the typical quantity accessed in ac susceptibility imaging experiments, using either scanning Hall probes or SQUIDs. 3,8,9,33 This quantity was calculated for different values of Λ and Λ v , covering 0.05a ≤ |Λ ac | ≤ 2.5a, at a height z 0 = 0.005a above the plane of the strip. This value for z 0 is close to the typical probe height used in our experiments.…”

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Probing the low-frequency vortex dynamics in a nanostructured superconducting strip

et al. 2016

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We investigate by scanning susceptibility microscopy the response of a thin Pb strip, with a square array of submicron antidots, to a low-frequency ac magnetic field applied perpendicularly to the film plane. By mapping the local permeability of the sample within the field range where vortices trapped by the antidots and interstitial vortices coexist, we observed two distinct dynamical regimes occurring at different temperatures. At a temperature just below the superconducting transition, T /Tc = 0.96, the sample response is essentially dominated by the motion of highly mobile interstitial vortices. However, at a slightly lower temperature, T /Tc = 0.93, the interstitial vortices freeze up leading to a strong reduction of the ac screening length. We propose a simple model for the vortex response in this system which fits well to the experimental data. Our analysis suggests that the observed switching to the high mobility regime stems from a resonant effect, where the period of the ac excitation is just large enough to allow interstitial vortices to thermally hop through the weak pinning landscape produced by random material defects. This argument is further supported by the observation of a pronounced enhancement of the out-of-phase response at the crossover between both dynamical regimes.

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“…The local dissipation can be inferred from the phase lag between the vortex motion and the driving force induced by an oscillatory magnetic field, whereas the amplitude of the oscillatory vortex motion provides us with information about the shape of the local potential that each fluxon experiences. This method has permitted us to reveal the contribution of pinning-driven (thermally activated) dissipative vortex motion [3], to demonstrate the nondissipative nature of the Meissner as well as the dissipative vortex state at microscopic scale [3] and finally, to obtain a detailed cartography of the distribution and intensity of the pinning landscape [2,4]. This technique not only shed new light on unraveling the basic mechanisms of vortex dissipation with unmatched resolution, but it permitted one to validate the theoretical models introduced to explain the measured integrated ac vortex responses in ac-susceptibility experiments [5].…”

Section: General Introduction To Ac Susceptibilitymentioning

confidence: 99%

2. Probing vortex dynamics on a single vortex level by scanning ac-susceptibility microscopy

Vondel¹,

Raes²,

Silhanek³

et al. 2017

Superconductors at the Nanoscale

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The low-frequency response of type II superconductors to electromagnetic excitations is the result of two contributions: the Meissner currents and the dynamics of quantum units of magnetic flux, known as vortices. These vortices are threedimensional elastic entities, interacting repulsively, and typically immersed in an environment of randomly distributed pinning centers. Despite the continuous progress made during the last decades, our current understanding of the complex dynamic behavior of vortex ensembles relies on observables involving a statistical average over a large number of vortices. Global measurements, such as the widespread acsusceptibility technique, rely on introducing certain assumptions concerning the average vortex motion thus losing the details of individuals. Recently, scanning susceptibility microscopy (SSM) has emerged as a promising technique to unveil the magnetic field dynamics at local scales. This chapter is aimed at presenting a pedagogical and rather intuitive introduction to the SSM technique for uninitiated readers, including concrete illustrations of current applications and possible extensions.

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Closer look at the low-frequency dynamics of vortex matter using scanning susceptibility microscopy

Cited by 11 publications

References 42 publications

Conformal Vortex Crystals

Conformal Vortex Crystals

Probing the low-frequency vortex dynamics in a nanostructured superconducting strip

2. Probing vortex dynamics on a single vortex level by scanning ac-susceptibility microscopy

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