Experimental observation of high-field diamagnetic fluctuations in niobium

Salem‐Sugui, S.; Friesen, Mark; Alvarenga, A. D.; Gandra, F. G.; Doria, Mauro M.; Schilling, Osvaldo F.

doi:10.1103/physrevb.66.134521

Cited by 16 publications

(15 citation statements)

References 21 publications

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“…This rounding effect masking the second order phase transition was observed in all curves obtained for fields above 20 kOe, and it is more pronounced in the sample with T c =28 K. This rounding is reminiscent of high-field diamagnetic fluctuations observed in high-T c superconductors which have been extensively studied [21,22,23,39,40]. It should be mentioned that a similar but less pronounced rounding effect have also been observed in Nb with κ = 4 [27], which is a well know BCS superconductor. It is important to mention that, since the rounding effect in the higher field curves extends above T c which is defined here at the onset of diamagnetic signal, we discard the possibility of the rounding effect to be influenced by sample inhomogeneity.…”

Section: Resultssupporting

confidence: 62%

“…In the case of layered systems, fluctuation superconductivity is enhanced, and there are robust theories predicting the behavior of many measurable quantities with temperature and magnetic field, in or out of the critical region [17,20,21,22,23,24,25,26]. Comparison of experimental results with these theories helps to understand the nature of the fluctuations, its dimensionality [18,23,27,28,29] and give additional insight about the pairing mechanism symmetry of the studied system [24,30].…”

Section: Introductionmentioning

confidence: 99%

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Superconducting fluctuations in the reversible magnetization of the iron-pnictideBa1−xKxFe2As

et al. 2009

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We report on isofield magnetization curves obtained as a function of temperature in two single crystals of Ba1−xKxF e2As2 with superconducting transition temperature Tc=28K and 32.7 K. Results obtained for fields above 20 kOe show a well-defined rounding effect on the reversible region extending 1-3 K above Tc(H) masking the transition. This rounding appears to be due to threedimensional critical fluctuations, as the higher field curves obey a well know scaling law for this type of critical fluctuations. We also analyzed the asymptotic behavior of √ M vs.T curves in the reversible region which probes the shape of the gap near Tc(H). Results of the analysis suggests that phase fluctuations are important in Ba1−xKxF e2As2 which is consistent with nodes in the gap.

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Section: Resultssupporting

confidence: 62%

Section: Introductionmentioning

confidence: 99%

Superconducting fluctuations in the reversible magnetization of the iron-pnictideBa1−xKxFe2As

et al. 2009

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“…Therefore, away from the glass line, the two quantities have the LLL scaling as was demonstrated, for example, by several experiments on YBCO for both magnetization 55 and conductivity, 56 while near the glass line ͑experimentally determined in Ref. 57͒, the scaling is violated.…”

Section: Discussionmentioning

confidence: 83%

Quantitative theory of transport in vortex matter of type-II superconductors in the presence of random pinning

Rosenstein

Zhuravlev

2007

Phys. Rev. B

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We quantitatively describe the competition between interactions, thermal fluctuations, and random quenched disorder using the dynamical Martin-Siggia-Rose approach ͓Phys. Rev. A 8, 423 ͑1973͔͒ to the Ginzburg-Landau model of the vortex matter. The approach first used by Dorsey et al. ͓Phys. Rev. B 45, 523 ͑1992͔͒ to describe the linear response far from H c1 is generalized to include both pinning and finite voltage. It allows one to calculate the non-Ohmic I-V curve, thereby extending the theory beyond the linear response. The static flux line lattice in type-II superconductors undergoes a transition into three disordered phases: the vortex liquid ͑not pinned͒, the homogeneous vortex glass ͑pinned, if one disregards an exponentially small creep at finite tem-peratures͒, and the crystalline Bragg glass ͑pinned͒ due to both thermal fluctuations and disorder. The location of the glass transition line in the homogeneous phase is determined and compared to experiments. The line is clearly different from both the melting line and the second peak line describing the translational and rotational symmetry breaking at high and low temperatures, respectively. Time correlation and response functions of the order parameter as functions of the time difference are calculated in both the liquid and the amorphous homogeneous phases. They determine the relaxation properties of the vortex matter due to the combined effect of pinning and thermal fluctuation. We calculate the critical current as a function of magnetic field and temperature in the homogeneous phase. The surface in the J-B-T space defined by this function separates between a dissipative moving vortex matter regime and vortex glass. A quantitative theory of the peak effect, qualitatively different from the conventional one due to Pippard ͓C.

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“…( Nishizaki et al, 2000) and with N b (after correction to a rather small κ) to data of ref. (Salem-Sugui et al, 2002), while the specific heat data were compared with experimental in SnN b 3 in ref. (Lortz et al, 2006) and in N b (also after the finite κ correction).…”

Section: Magnetization and Specific Heat In Vortex Liquidsmentioning

confidence: 99%

Ginzburg-Landau theory of type II superconductors in magnetic field

2010

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Thermodynamics of type II superconductors in electromagnetic field based on the GinzburgLandau theory is presented. The Abrikosov flux lattice solution is derived using an expansion in a parameter characterizing the "distance" to the superconductor -normal phase transition line. The expansion allows a systematic improvement of the solution. The phase diagram of the vortex matter in magnetic field is determined in detail. In the presence of significant thermal fluctuations on the mesoscopic scale (for example in high Tc materials) the vortex crystal melts into a vortex liquid. A quantitative theory of thermal fluctuations using the lowest Landau level approximation is given. It allows to determine the melting line and discontinuities at melt, as well as important characteristics of the vortex liquid state. In the presence of quenched disorder (pinning) the vortex matter acquires certain "glassy" properties. The irreversibility line and static properties of the vortex glass state are studied using the "replica" method. Most of the analytical methods are introduced and presented in some detail. Various quantitative and qualitative features are compared to experiments in type II superconductors, although the use of a rather universal Ginzburg -Landau theory is not restricted to superconductivity and can be applied with certain adjustments to other physical systems, for example rotating Bose -Einstein condensate.

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Experimental observation of high-field diamagnetic fluctuations in niobium

Cited by 16 publications

References 21 publications

Superconducting fluctuations in the reversible magnetization of the iron-pnictideBa1−xKxFe2As

Superconducting fluctuations in the reversible magnetization of the iron-pnictideBa1−xKxFe2As

Quantitative theory of transport in vortex matter of type-II superconductors in the presence of random pinning

Ginzburg-Landau theory of type II superconductors in magnetic field

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