Superconducting order parameter fluctuations above Tc in polycrystalline Ho1Ba2Cu3O7−δ compounds

The conductivity and the magnetization around Tc in optimally-doped YBa$_2$Cu$_3$O$_{7-δ}$ revisited: quantitative analysis in terms of fluctuating superconducting pairs

“…We have checked that the T onset value determined from our resistivity measurements by using a background-independent procedure agrees, well within the corresponding experimental uncertainties, with those that may be inferred from the measurements of other research groups in the best available OPT Y-123 single-crystals and epitaxial films. [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][28][29][30][31][32][33][34][35] Similarly, we have checked that the T onset we propose here from our magnetization measurements in the zero-field limit agrees with the results on the precursor diamagnetism onset that may be inferred from the χ(T ) H measurements of other authors in single-crystal and polycrystalline OPT Y-123 superconductors. [8][9][10][39][40][41] The conductivity and the magnetization around T c in OPT Y-123...…”

“…The conductivity and the magnetization around T c in OPT Y-123... microbridge studied in the previous subsection are well within the dispersion expected for different high-quality OPT Y-123 samples. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][28][29][30][31][32][33][34][35][36][37][38][39][40][41] The magnetic susceptibility rounding above T c , that following the conventional denomination will already be called precursor diamagnetism, is orders of magnitude smaller than in the Meissner region. [3,8] Therefore, to measure these roundings one must apply magnetic fields orders of magnitude larger than those used in the ZFC measurements.…”

“…This arises from the failure at low fields of the LLL approximation used by Eq. (18). At H = 0, the width of the full-critical region (where the mean-field-like approaches are no longer applicable and the superconducting fluctuations are described instead in terms of the XY model) may be approximated by the well-known Ginzburg criterion originally calculated for 3D superconductors by Levanyuk [139] and Ginzburg [140] (for an extension to layered superconductors, see Ref.…”

“…In fact, in a wide temperature interval, above but not too close to T c (above the so-called Ginzburg-Levanyuk temperature) and well below the rounding onset temperature, these effects in OPT HTSC were well described in terms of the phenomenological mean-field Gaussian-Ginzburg-Landau (GGL) approach for the superconducting fluctuations of both the amplitude and the phase of the order parameter in multilayered superconductors [3][4][5][6][7][8]. This conclusion was supported, e.g., by measurements of the magnetization rounding above T c (the socalled precursor diamagnetism) [7][8][9][10] and of the in-plane electrical resistivity rounding (the so-called paraconductivity) [7,8,[11][12][13][14][15][16][17][18][19][20][21][22][23][24]. These two observables are not only crucial to characterize the superconducting transition but, in addition, in HTSC they present an excellent ratio between the extent of the rounding effects and the corresponding background or bare contributions (orders of magnitude bigger than, for instance, in the heat capacity) [3,8].…”

Structural and Fluctuation Induced Excess Conductivity in R:1113 Superconductors

“…Gaussian fluctuation is probably dominant in the temperature region above the mean field temperature T c mf when the fluctuation in the order parameter is small and the interactions between Cooper pairs can be neglected, while the critical fluctuation occurs in the critical field region below the T c mf when the fluctuations in the order parameter are large and the interactions between Cooper pairs is considered. The variation of Gaussian fluctuation-induced conductivity with the reduced temperature helps the researchers to find the dimensional exponents, coherence length, and crossover temperatures [15,16]. The dimensional exponents in high T c materials are found to be zero-dimensional (0D), onedimensional (1D), two-dimensional (2D), and threedimensional (3D).…”