Two coexisting vortex phases in the peak effect regime in a superconductor

Marchevsky, M.; Higgins, M. J.; Bhattacharya, S.

doi:10.1038/35054512

Cited by 120 publications

(143 citation statements)

References 14 publications

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“…By magnetic measurements, we have no information about the order of the transition. We detected magnetic history effects (which will be reported elsewhere), for temperature lower than the peak temperature (T p ), as in other type II superconductors [24,25,28], but they are not a proof of a first order transition. Recent calorimetric measurements [29], in fact, show that the latent heat is zero around T p , suggesting that it cannot be a first order transition.…”

Section: Fig 1 Detection Of the Peakmentioning

confidence: 52%

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

et al. 2006

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We report additional experimental evidences about the presence of an universal behavior in the Field-Temperature Phase Diagram of Type II Superconductors. This behavior is characterized by a phase transition in the vortex matter between the disordered and the Bragg Glass phase. The experimental detection of a Peak Effect phenomenon has been proved to be strictly connected to the existence of this phase transition. In this paper, we show the first observation of a Peak Effect in the compound Nb 3 Sn, by using 1 st harmonics of the AC magnetic susceptibility. Peak Effect has been detected at fields between 3T and 13T, whereas it is not observable at higher fields. This seems to be in contrast with the theoretical predictions of such a phase transition at all fields and, therefore, with the predicted universality in the magnetic behavior of the Type II superconductors. Nevertheless, by measuring the 3 rd harmonics of the AC susceptibility, this phase transition has been detected up to our highest available field (19 T), thus demonstrating the necessity of the higher harmonics analysis in studying these topics and moreover proving the validity of the theoretical predictions. Magnetic flux penetrates a type II superconductor in form of vortices, which distribute in a regular lattice in absence of defects [1,2]. Defects affect the lattice ordering, but prevent the dissipations associated to the vortex movement [2]. An universal field-temperature phase diagram has been supposed for all the type II superconductors with point defects. In this phase diagram a transition in the vortex lattice has been predicted, between a disordered phase and the Bragg Glass Phase [3,4]. This latter is characterized by a quasi long range order and a perfect topological order, in which the vortex lattice stills survives despite the presence of the pinning [3], as it has also been experimentally evidenced [5]. The disordered phase has been supposed to be again a glass phase ("multidomain glass"), but with a topological disorder at the largest length scales [4]. The critical current density, J c [6], generally decreasing with increasing temperature and/or magnetic field [2], shows a local maximum, known as Peak Effect [7], when the Disordered/Bragg Phase transition occurs. For this reason, the observation of the Peak Effect has been widely used to detect this phase transition [3]. The Peak Effect has been evidenced in various classes of type II superconductors, e.g. low-T c [8][9][10][11][12], high-T c [13][14][15], boro-carbides [16] and MgB 2 [17]; however, it has not been observed in Nb 3 Sn up to the present day, to the best of our knowledge. Nb 3 Sn crystallizes in the A15 type structure and is actually the most used material in the manufacturing of superconducting magnets at very high fields [18]. In the present work, measurements have been performed on a high quality Nb 3 Sn single crystal, furnished by M. Toyota [19] (Dimensions ≈ 3 x 1.32 x 0.43 mm 3 ). The sample was characterized by T c = 18.2 K, ΔT c = 0.1 K, T m = 38.84 K. A valu...

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Section: Fig 1 Detection Of the Peakmentioning

confidence: 52%

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

et al. 2006

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“…While the result and interpretation for Nb is controversial [10], in (K,Ba)BiO 3 the regime below T p (H) is interpreted as a quasi-lattice or Bragg glass [7,8] where disorder was shown to be significantly reduced by adding a small oscillatory component to the field while cooling. This is also reminiscent of the well-known orderdisorder coexistence seen for the corresponding regime in anisotropic 2H-NbSe 2 [16,17,18]. A direct way to examine the possibility of BSFF is through the direct application of transport current and observing the voltage-current V(I) response in light of equation (1).…”

Section: Resultsmentioning

confidence: 99%

Electrical transport, magnetic, and structural properties of the vortex lattice ofV3Siin the vicinity of the peak effect

et al. 2003

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The peak effect in critical current density J c is investigated by studying the flux dynamics in V 3 Si using bulk magnetometry, small-angle neutron scattering, and transport measurements on clean single-crystal samples from the same ingot. For a field-cooled history, well-defined structure in the vortex lattice was found for fields and temperatures (H,T) below the peak-effect line H P (T); above this line, the structure disappeared. History-dependent, metastable disorder is found only for (H,T) below H P (T) but thevortex system is reproducibly re-ordered either by field-cooling or a low-frequency, pulsed "shaking" transport current. The latter is shown to attain Bardeen-Stephen flux flow. In addition, flux flow is observed at H P (T) at high current levels. The results support the traditional picture of H P (T) as an order-disorder transition due to the competition between elasticity and pinning.

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“…[11], where the voltage noise was attributed to the dynamical annealing of a disordered vortex phase nucleated close to the edges. We stress that this latter interpretation was proposed for the peculiar case of the peak effect in N bSe 2 , where two macroscopic critical current states coexist in the sample ( [12,13] and references herein), and where the large noise values are coming from the kinetic between these two states. This was shown to correspond to non-Gaussian noise by a second spectrum analysis [14].…”

Section: Resultsmentioning

confidence: 99%

Experimental study of the correlation length of critical-current fluctuations in the presence of surface disorder: Probing vortex long-range interactions

Scola¹,

Pautrat²,

Goupil³

et al. 2006

Phys. Rev. B

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We report on critical currents and voltage noise measurements in Niobium strips in the superconducting state, in the presence of a bulk vortex lattice (B < BC2) and in the surface superconducting state (Bc2 < B < BC3). For homogeneous surfaces, the correlation length of the current fluctuations can be associated with the electromagnetic skin depth of vortex superficial instabilities. The modification of the surface state by means of low energy irradiation induces a strong modification of the critical current and of the noise. The appearance of a corner frequency in the spectral domain can be linked with the low wave-vectors of the artificial corrugation. Since this latter occurs only for B < BC2, we propose that the long-range interactions allow the correlation length to extend up to values imposed by the surface topography.PACS numbers: 71.27.+a,72.70.+m,72.20.My Noise measurements are powerful tools to go inside the origin of the vortex pinning, and of the dynamical interactions between the vortex lattice and the sample disorder. This noise, generated during the lattice flow, is called the flux-flow noise [1]. It is generally characterized by the shape of its spectral density, and by its power. As it is often proposed in noise analysis, it is convenient to define a correlation length, within which the fluctuations are correlated. This defines the fluctuator of the system. To the extent that the fluctuators are independent and that the system is large enough, the correlation length can be calculated from the noise power via an usual statistical averaging (the central limit theorem) [2]. Recently, it was shown that no difference can be observed between the flux-flow noise in the mixed state and in the surface superconducting state of a Niobium slab [3]. In other words, the same fluctuator is present with or without a bulk vortex lattice, showing clearly its superficial origin. The coupling to the bulk was shown to be due to the conservation of the total current. This confirms previous auto and cross correlation experiments of both flux and voltage noises [4], and explains the insensivity of the low frequency noise to bulk perturbations [5], in Pb-In alloys. In these experiments, two parameters, the normalized spectrum of the fluctuator and its correlation length, are experimentally justified but are not explained [3,4]. If the fluctuator is of superficial origin, it should be possible to induce notable changes in the noise characteristics after some surface treatments. A following change in the noise spectral density, the noise power, or eventually in the underlying statistics, would give some clues to understand the spectrum and the fluctuator origins. Wherever it takes place, it has been made clear for years that the existence of flux-flow noise is intimately linked to the nature of the relevant disorder, i.e. to the vortex pinning. In the conclusion of his review article, Clem states that such a flux-flow noise theory " should be intimately related to an appropriate theory of critical current density " [1]...

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Two coexisting vortex phases in the peak effect regime in a superconductor

Cited by 120 publications

References 14 publications

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

Transition between the Bragg glass and the disordered phase inNb3Sndetected by third harmonics of the ac magnetic susceptibility

Electrical transport, magnetic, and structural properties of the vortex lattice ofV3Siin the vicinity of the peak effect

Experimental study of the correlation length of critical-current fluctuations in the presence of surface disorder: Probing vortex long-range interactions

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