Resistive Transitions and Surface effects in Type-II Superconductors

Hempstead, C. F.; Kim, Y. B.

doi:10.1103/physrevlett.12.145

Cited by 188 publications

(56 citation statements)

References 7 publications

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“…1 middle), which are characteristics a surface superconducting state [18]. All the departure from the Ohmic normal state behavior is due to these surface currents [19]. At the same time, the differential resistance R is dV /dI ≈ R n at high current even if the normal state is not reached, as simply state by V /I = R n ( fig.…”

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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“…However, under a low applied current, the electric resistance reaches its normal state value R n at much higher field, and hysteric magnetization is also observed up to B c3 ≈1.7 B c2 due to the existence of a finite critical current in the surface superconducting (SSC) state [17][18][19]. From V(I) curves (not shown here), we find that the differential resistance dV/d(I-I c )≈ R n as soon as B>B c2 as expected for a metallic bulk [14,20]. Then, from these different measurements, it is possible to identify both critical fields B c2 and B c3 at different temperatures.…”

Section: Resultsmentioning

confidence: 87%

Change of surface critical current in the surface superconductivity and mixed states of superconducting niobium

Aburas

Pautrat

Bellido

2016

Supercond. Sci. Technol.

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A systematic study of irreversible magnetization was performed in bulk Niobium after different surface treatments. Starting with smooth surfaces and abrading them, a strong increase of the critical current is observed up an apparent limiting value. An impressive change of the critical current is also observed in the surface superconductivity (SSC) state, reaching values of the same order of magnitude as in the mixed state. We explain also the observation of strong SSC for magnetic field perpendicular to larges facets in terms of nucleation of SC along bumps of a corrugated surface.

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“…Therefore, the quadratic term dominates the field dependence which deviates from the linear behavior predicted by the Bardeen-Stephen theory. 12,13 This is not surprising, considering that the Bardeen-Stephen theory is valid only at zero temperatures or in the zero-magnetic-field limit at finite temperatures. Fig.…”

Section: -mentioning

confidence: 99%

Magnetic pinning of flux lattice in superconducting-nanomagnet hybrids

Lara

Castaño

et al. 2011

Applied Physics Letters

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Strong superconducting pinning effects are observed from magnetic landscapes produced by arrays of circular rings with varying magnetic remanent states. The collective and the background pinning of superconducting Nb films is strongly enhanced by the stray magnetic field produced by an array of circular Ni rings magnetized to form "onion" (bidomain) states. On the other hand, when the same rings are magnetized into vortex (flux-closed) states, or are randomly magnetized, the superconducting pinning is much smaller. The greatest pinning is produced when the superconducting vortex lattice motion is along a direction in which there is a strong magnetic field variation. Vortices occur in a wide range of quantum fluids. 1,2 Due to their mutual interactions, superconducting vortices order into regular vortex lattices in defect-free materials. The structure and dynamics of the vortex lattice is significantly affected by interactions with intrinsic and extrinsic artificially prepared pinning centers. The motion of the normal cores of superconducting vortices produces dissipation. This plays a key role in superconductor properties such as fluxflow resistance, critical currents, magnetization, and magnetic susceptibility. These properties are important ingredients in superconductor based applications.The effect of magnetic pinning centers has been investigated using a variety of techniques, 3 and the influence of magnetic domains and domain walls on various superconducting properties has been reported. [4][5][6][7] In spite of this, no clear-cut experimental evidence has emerged to prove that magnetic interaction between the superconducting vortices and magnetic pinning centers plays a determining role. We show here, by manipulating the magnetic state of a pinning array of magnetic nanorings, the magnetotransport of superconducting films can be controlled and changed substantially. Previously, 8 we studied ratchet effects in similar samples to investigate the role played by magnetic potentials with broken reflection symmetry on the vortex lattice dynamics.In this work, we have studied the magnetism and magnetotransport of hybrid superconducting Nb thin films grown on top of square-symmetry arrays of circular magnetic Ni rings [see Figure 1(a) for dimensions]. The Ni rings were prepared by electron-beam lithography on (100) Si substrates as described elsewhere. 9 The 20 nm thick Ni film was deposited by ion-beam sputtering while the 100 nm Nb was magnetron-sputtered. Nb electrical contacts were patterned to form a 40 lm Â 40 lm bridge.The magnetic hysteresis of the rings was measured using alternating gradient force magnetometry. A similar array of Ni rings without a Nb layer was studied by atomic force microscopy [AFM, Fig. 1(a)], magnetic force microscopy [MFM, Fig. 1(b)], and magneto-optical Kerr effect (MOKE, Fig. 2) using the first-order reversal curve (FORC) method. 10 The 30 lm diameter MOKE laser beam probed approximately 10 3 rings simultaneously. Micromagnetic simulations were performed using the 2D OOMMF code 11...

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Resistive Transitions and Surface effects in Type-II Superconductors

Cited by 188 publications

References 7 publications

Voltage noise and surface current fluctuations in the superconducting surface sheath

Voltage noise and surface current fluctuations in the superconducting surface sheath

Change of surface critical current in the surface superconductivity and mixed states of superconducting niobium

Magnetic pinning of flux lattice in superconducting-nanomagnet hybrids

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