Depinning Transition in Type-II Superconductors

Lütke-Entrup, N.; Plaçais, Bernard; Mathieu, P.; Simon, Y.

doi:10.1103/physrevlett.79.2538

Cited by 30 publications

(49 citation statements)

References 15 publications

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“…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.…”

mentioning

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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mentioning

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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“…Such experiments are aimed at testing theories of vortex phases in the presence of quenched disorder, 1,2 surface pinning, 3 columnar defects produced by heavy-ion irradiation, 4 and, more recently, nanoengineered periodic pinning arrays. 5 For specimens with random point defects as the main source of pinning, the linear response is usually well accounted for by a single-particle model, 6,7 which describes small oscillations of vortices by the equation of motion u ϭϪ␣ L uϩF ac ͑ t ͒,…”

Section: Introductionmentioning

confidence: 99%

Linear ac dynamics of vortices in a periodic pinning array

Silva

Aguiar

Moshchalkov³

2003

Phys. Rev. B

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The vortex-dominated ac response of a superconducting film with a periodic array of pinning centers is studied in the linear regime for vortex densities greater than the saturation number. A simple model is introduced to describe small oscillations of the vortex lattice, which is considered to be composed of two distinct lattices formed by trapped vortices and interstitial vortices. The frequency-dependent complex resistivity is calculated as a function of frequency and magnetic induction for vortex densities between the first and the second matching fields. It is shown that the absorption spectra has two peaks corresponding to two characteristic pinning frequencies: one due to the periodic pinning array and another due to vortex-cage pinning. The range of validity of the model is determined from direct numerical simulations.

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“…A typical depinning spectrum is shown in the figure 1. It follows closely, over the whole frequency range, the two modes model of surface vortex pinning developed in [4,5]. At the same time, it was impossible to perform acceptable fits using bulk pinning models.…”

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confidence: 99%

The vortex depinning transition in untwined YBaCuO using complex impedance measurements

Pautrat¹,

Goupil²,

Simon³

et al. 2004

Physica C: Superconductivity

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We present surface impedance measurement of the vortex linear response in a large untwinned YBCO crystal. The depinning spectra obtained over a broad frequency range (100 Hz-30 MHz) are those of a surface pinned vortex lattice with a free flux flow resistivity (two modes response). The critical current in the "Campbell" like regime and the flux flow resistivity in the dissipative regime are extracted. Those two parameters are affected by the first order transition, showing that this transition may be related to the electronic state of vortices.The linear ac response of a pinned vortex lattice has been observed in the 60's in conventional type II superconducting materials [1]. At low frequencies, say f 1 KHz, a small ac field has an apparent penetration characterized by a static regime without any loss (the Campbell regime). It has been recognized as a direct consequence of the vortex pinning, and disagrees with first interpretations based on thermally activated depinning [2]. Note that this linear regime is not the ohmic regime of a vortex lattice free from any pinning (the so called liquid phase). At the same time, the high frequency response (f 1-10 MHz) is that of a medium with a free resistivity (skin effect). Those two regimes are separated by the depinning frequency, and the shape of the whole spectrum allows to discriminate between different types of pinned vortex states. One of the main interest of this method is that vortex states can be studied even in the presence of a large critical current. The principle of the experiment is to measure the ac penetration length, due to the vortex response, in a small coil directly glued around the sample. The detailed experimental procedure can be found in [3]. A typical depinning spectrum is shown in the figure 1. It follows closely, over the whole frequency range, the two modes model of

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Depinning Transition in Type-II Superconductors

Cited by 30 publications

References 15 publications

Voltage noise and surface current fluctuations in the superconducting surface sheath

Voltage noise and surface current fluctuations in the superconducting surface sheath

Linear ac dynamics of vortices in a periodic pinning array

The vortex depinning transition in untwined YBaCuO using complex impedance measurements

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