Studies of Surface Transport Currents in Type-II Superconductors; a Surface-Flux-Pinning Model

Hart, H. R.; Swartz, P.S.

doi:10.1103/physrev.156.403

Cited by 92 publications

(39 citation statements)

References 43 publications

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“…It is very likely that the local surface disorder acts as the pinning potential for this short vortices ( [16] and references herein), leading to a surface critical state. Therefore, the associated superficial critical current i c (A/m) comes from a pinning mechanism, and is consequently observed lower than its theoretical upper bound [17]. For I ≥ I c ≈ 2W.i c (W=width), surface vortex depinning occurs.…”

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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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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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“…Similarly, when the field is tilted within the side faces the surface superconducting state is not suppressed, and the only observed angular dependence arises from the intrinsic anisotropy of MgB 2 . Furthermore, non-Ohmic transport properties above the bulk upper critical field are expected due to the presence of a surface critical current, I sc , [20]. If the applied current is smaller than I sc then the resistance will go to zero above H c2 (T c2 ), see Fig.…”

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“…dependence for field around the c axis and studies on PbTl films and ribbons [20] that have shown that the angular dependence is sharper for smooth surfaces. In addition, due to the anisotropy of the coherence length, the thickness of the current carrying layer at the top and bottom faces is about four times smaller than along the side faces.…”

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confidence: 99%

“…A superconducting surface sheath with a thickness given by the Ginzburg-Landau coherence length, ξ(T ), nucleates at an enhanced field of H c3 = 1.69H c2 when a magnetic field is applied parallel to the flat (infinite) surface of an isotropic superconductor [16]. The exact value of the enhancement factor may depend on clean-limit corrections [17], on the shape of the sample and its intrinsic anisotropy [18], and on the surface quality [20].…”

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Surface contribution to the superconducting properties ofMgB2single crystals

et al. 2003

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We demonstrate direct evidence of possible surface superconductivity on small, well-shaped MgB2 single crystals. Transport measurements in the range H < 1.6H c c2 , where H c c2 is the bulk upper critical field for the c axis, show non-Ohmic and strongly angular dependent resistivity. Studies of the alignment of H with selected crystal surfaces, transport and specific heat measurements on the same crystal, and a physical sculpturing of the crystal surfaces using a focused ion beam all support the conclusion. Similar, albeit less pronounced results are obtained for fields in the basal plane.

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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].…”

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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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Studies of Surface Transport Currents in Type-II Superconductors; a Surface-Flux-Pinning Model

Cited by 92 publications

References 43 publications

Voltage noise and surface current fluctuations in the superconducting surface sheath

Voltage noise and surface current fluctuations in the superconducting surface sheath

Surface contribution to the superconducting properties ofMgB2single crystals

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

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