Paraconductivity of oxygen-deficient YBa₂Cu₃O_xthin films

Abstract

The paraconductivity of a number of c-axis-oriented YBa2Cu3Ox thin films, with a range of c-axis lattice parameters and Tc-values, has been determined as a function of temperature and analysed in terms of the paraconductivity due to direct and indirect fluctuation contributions. We present results on the c-axis coherence length and the phase-relaxation time at 100 K obtained from the fit to the paraconductivity data. The paraconductivity results for optimally doped films were: c-axis coherence length: ξc(0) = 1.25 Å; pair-breaking parameter: δ = 0.05; phase-relaxation time at 100 K: τϕ = 0.066 ps; and two-three-dimensional crossover temperature: T+ = 96.6 K. These values are in good agreement with those from other published work. There was considerable scatter in the coherence length and phase-relaxation time for films with different critical temperatures and oxygen contents. These results were process dependent but appear to be related to the 60 K phase transition in the Tc-x phase diagram.

In-plane paraconductivity inLa2−xSrxCuOCurrás1, Ferro2, González3 et al. 2003Phys. Rev. B4010380View full textAdd to dashboardCite

“…In fact, once σ ab (T, x) is measured, the above question is equivalent to ask how ∆σ ab (T, x) is affected by doping. This last question was first addressed by Suzuki and Hikita [4] and by Cooper and coworkers [5], and since then by different authors [6,7,8,9,10,11,12,13,14]. However, as of today some of the main conclusions (including, e.g., the dimensionality of the fluctuations or the influence of the normalstate pseudogap) are still not well settled or they are even contradictory.…”

“…[6][7][8][9][10][11][12][13][14] However, as of today some of the main conclusions ͑including, e.g., the dimensionality of the fluctuations or the influence of the normal-state pseudogap͒ are still not well settled or are even contradictory. For instance, in the case of YBa 2 Cu 3 O x ͑YBCO͒, some authors 5,8,13 proposed that ⌬ ab becomes more three dimensional ͑3D͒ when x increases, whereas other authors 6,11 did not find any appreciable dimensionality variation. Also, other authors have proposed, by analyzing either the fluctuation magnetization 14 or the thermal expansion, 12 that the superconducting fluctuations in underdoped YBCO do not follow the Gaussian mean-field-like theories used in Refs.…”

“…Also, other authors have proposed, by analyzing either the fluctuation magnetization [14] or the thermal expansion [12], that the superconducting fluctuations in the underdoped YBCOx do not follow the Gaussian mean-field-like theories used in Refs. [5,6,8,11,13] but follow instead different forms of non-Gaussian fluctuations. [12,14] Another example of these discrepancies is provided by the studies of La 2−x Sr x CuO 4 (LSxCO): By analyzing their measurements of the in-plane conductivity and magnetoconductivity, Suzuki and Hikita [4] proposed a change in dimensionality (2D to 3D) as doping increases from underdoped (x < 0.15) to overdoped (x > 0.15).…”

“…A second source of ambiguity is the probable presence in some of the samples of structural and stoichiometric inhomogeneities which, even when they are relatively small, may appreciably affect the measured σ ab (T, x), mainly near T C . [27] Third, some authors [4,11] analyze their ∆σ ab (T, x) data in terms of the direct Aslamazov-Larkin (AL) contributions plus a pair-breaking (Maki-Thompson, MT) term, while others [6,8,9,10,13] take into account only the AL contributions, and yet others [5,7] do not decide between both possibilities. Finally, a fourth source of ambiguity is that the region of reduced-temperatures, ε ≡ ln(T /T C ), where the data are analyzed was relatively small, typically 10 −2 < ∼ ε < ∼ 0.1, due to the fact that the conventional GGL approach is not applicable very near or very far away from T C .…”

Superconducting fluctuation behavior and infrared absorption properties of Tl1−Cu Sr1.6Yb0.4CaCu2O7 and Tl0.5Pb0.5Sr2−Mg Ca0.8Yb0.2Cu2O7− ceramics

“…However, it has been shown [27] that for polycrystalline samples, due to the non-uniform current flow, the coherence length, c (0) can be more precisely calculated using the Lawrence-Doniach-based equations below:…”