Fluctuation-induced diamagnetism at high reduced temperatures in YBa
 2
 Cu
 3
 O
 7 − δ
 superconductors

Mosqueira, J.; Carballeira, C.; Ramallo, M. V.; Torrón, C.; Veira, J.A.; Vidal, F.

doi:10.1209/epl/i2001-00199-0

Cited by 36 publications

(74 citation statements)

References 22 publications

(20 reference statements)

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“…1). Under these very low fields, the superconducting fluctuation effects are expected to be negligible 3,4,5,6,7,23,24,25 and, therefore, the observed susceptibility roundings above T C will be mainly due to inhomogeneities and disorder. As it may be appreciated, the Meissner transition is very sharp, the transition temperature width, defined as usually, 21 being around ∼ 1 K, and the zero-field critical temperature T C0 = 122.0 K. These data also show an exceptionally high Meissner fraction, |χ F C (T → 0)| ≈ 0.8.…”

Section: Experimental Details and Resultsmentioning

confidence: 99%

“…This last conclusion was supported by the fact that the measured diamagnetism could be accounted for in terms of the Ginzburg-Landau approach for multilayered superconductors with Gaussian fluctuations of the superconducting order parameter (GGL approach). Since then, the applicability of this conventional phenomenological GGL scenario, which was more recently extended empirically to high reduced temperatures by the introduction of a total energy cutoff, 5 has been confirmed by different groups in many HTSC, 6,7 very in particular in underdoped compounds up to relatively high reduced field amplitudes, of the order of 0.2. 8,9 Further support was earlier provided by the consistency with other intrinsic rounding effects observed above T C , especially with the paraconductivity, 7,10 and also with the precursor diamagnetism in dirty low-T C superconductors.…”

Section: Introductionmentioning

confidence: 96%

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Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

2007

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The in-plane diamagnetism around the Meissner transition was measured in a Tl2Ba2Ca2Cu3O10 single crystal of high chemical and structural quality, which minimizes the inhomogeneity and disorder rounding effects on the magnetization. When analyzed quantitatively and consistently above and below the transition in terms of the Ginzburg-Landau (GL) approach with fluctuations of Cooper pairs and vortices, these data provide a further confirmation that the observed Meissner transition is a conventional GL superconducting transition in a homogeneous layered superconductor.

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Section: Experimental Details and Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 96%

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

2007

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“…The above results strongly suggest, therefore, that any superconducting fluctuation effect in the normal state will vanish above ε C . However, probably the best way to probe these results is to extend our first experiments on the fluctuation effects in the high-ε region [3,4] Fig. 1(b).…”

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confidence: 95%

On the consequences of the uncertainty principle on the superconducting fluctuations well inside the normal state

et al. 2002

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We first argue that the collective behaviour of the Cooper pairs created by thermal fluctuations well above the superconducting transition temperature, T C , is dominated by the uncertainty principle which, in particular, leads to a welldefined temperature, T C , above which the superconducting coherence vanishes. On the grounds of the BCS approach, the corresponding reduced-temperature, ε C ≡ ln(T C /T C ), is estimated to be around 0.55, i.e., above T C ≃ 1.7 T C coherent Cooper pairs cannot exist. The implications of these proposals on the superfluid density are then examined using the Gaussian-Ginzburg-Landau approximation. Then we present new measurements of the thermal fluctuation effects on the electrical conductivity and on the magnetization in different lowand high-T C superconductors with different dopings which are in excellent agreement with these proposals and that demonstrate the universality of ε C . 74.20.-z Theories and models of superconducting state 74.20.De Phenomenological theories (two-fluid, Ginzburg-Landau, etc.) 74.40.+k Fluctuations (noise, chaos, nonequilibrium superconductivity, localization, etc.)

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“…This behavior, which may be seen more clearly in the ⌬M͑H͒ T representation ͑see below͒, was already observed in other highly anisotropic superconductors 17,21 and may be attributed to a change of the fluctuation regime induced by the magnetic field. For temperatures and magnetic fields well above T C ͑H͒, the fluctuation magnetization of highly anisotropic superconductors when H Ќ ab predicted by the GL theory in the Gaussian approximation ͑GGL approach͒ and taking into account the total energy cutoff reads 17,[22][23][24] …”

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confidence: 99%

Fluctuation diamagnetism around the superconducting transition in a cuprate crystal with a reduced Meissner fraction

Mosqueira

Vidal

2008

Phys. Rev. B

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The magnetization around the superconducting transition was measured in a Tl 0.5 Pb 0.5 Sr 2 CaCu 2 O 7 crystal affected by a considerable reduction ͑ϳ55% ͒ of its effective superconducting volume fraction but still with a relatively sharp low-field Meissner transition, a behavior that may be attributed to the presence of structural inhomogeneities. By taking into account these inhomogeneities just through the Meissner fraction, the observed diamagnetism may still be explained, consistently above and below the superconducting transition, in terms of the conventional Ginzburg-Landau approach with fluctuations of Cooper pairs and vortices.The behavior of the magnetization around the Meissner transition provides an unavoidable constraint for any phenomenological description of a superconducting transition. 1 In the last few years, various groups have reported the observation of strong anomalies in the magnetization measured around the superconducting transition in high-T C cuprate superconductors ͑HTSCs͒ with different doping levels. Among these anomalies are the observation under low fields of giant diamagnetism ͓with amplitudes of orders of magnitude larger than the one associated with superconducting fluctuations in the conventional Ginzburg-Landau ͑GL͒ scenario͔ and a seemingly nonlinear temperature behavior of the associated upper critical field H C2 ͑T͒ near T C . 2-4 The origin of this unconventional ͑non-GL͒ behavior is at present a debated issue, 2-14 the proposals including T C inhomogeneities or vortex fluctuations even well above the measured T C . The interest of this debate is enhanced by the fact that it also concerns other open aspects of the HTSCs,such as the pseudogap in the normal state or the possible existence of a vortex fluid over a wide temperature range above T C . 14-16The magnetization measurements and analyses performed recently by our group in different HTSCs and dirty low T C superconductors ͑without nonlocal electrodynamic effects͒ favor the presence of extrinsic T C inhomogeneities, just associated with chemical inhomogeneities, as the origin of most of the observed magnetization anomalies. 4,12,17,18 Nevertheless, there is another very common type of inhomogeneity whose influence on the magnetization also deserves a close inspection: the one associated with structural defects at different length scales, including those as smaller as a few times the superconducting coherence length amplitude ͑0͒. In extreme type II superconductors, even these short length inhomogeneities, difficult to be directly observed, may strongly decrease the effective superconducting volume fraction without enlarging the temperature width of the low-field Meissner transition. In this Brief Report, we will first present detailed magnetization measurements around the Meissner transition in a Tl 0.5 Pb 0.5 Sr 2 CaCu 2 O 7 ͑TlPb1212͒ crystal deeply affected by a reduction of the effective volume fraction, an effect which does not enlarge the temperature width of the low-field Meissner transition and that may be a...

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Fluctuation-induced diamagnetism at high reduced temperatures in YBa ₂ Cu ₃ O _{7 − δ} superconductors

Cited by 36 publications

References 22 publications

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

On the consequences of the uncertainty principle on the superconducting fluctuations well inside the normal state

Fluctuation diamagnetism around the superconducting transition in a cuprate crystal with a reduced Meissner fraction

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Fluctuation-induced diamagnetism at high reduced temperatures in YBa 2 Cu 3 O 7 − δ superconductors

Cited by 36 publications

References 22 publications

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

Diamagnetism around the Meissner transition in a homogeneous cuprate single crystal

On the consequences of the uncertainty principle on the superconducting fluctuations well inside the normal state

Fluctuation diamagnetism around the superconducting transition in a cuprate crystal with a reduced Meissner fraction

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Fluctuation-induced diamagnetism at high reduced temperatures in YBa ₂ Cu ₃ O _{7 − δ} superconductors