Experimental observation of two-dimensional fluctuation magnetization in the vicinity ofTcfor low values of the magnetic field in deoxygenatedYBa2Cu3

Abstract

We have measured isofield magnetization curves as a function of temperature in two single crystal of deoxygenated YBaCuO with Tc = 52 and 41.5 K. Isofield magnetization curves were obtained for fields running from 0.05 to 4 kOe. The reversible region of the magnetization curves was analyzed in terms of a scaling proposed by Prange, but searching for the best exponent υ. The scaling analysis carried out for each data sample set with υ=0.669, which corresponds to the 3D-xy exponent, did not produced a collapsing of curves when applied to M vsT curves data obtained for the lowest fields. The resulting analysis for the Y123 crystal with Tc = 41.5 K, shows that lower field curves collapse over the entire reversible region following the Prange's scaling with υ=1, suggesting a two-dimensional behavior. It is shown that the same data obeying the Prange's scaling with υ=1 for crystal with Tc = 41.5 K, as well low field data for crystal with Tc = 52 K, obey the known two-dimensional scaling law obtained in the lowest-Landau-level approximation.

Onset of phase correlations inYBa2Cu3O7−xas determined from reversible-magnetization measurements

“…21 Indeed, deoxygenated crystals with the same transition temperatures studied here have previously been shown to exhibit strong 2D critical fluctuations. 22 The phase-mediated behavior of interest here occurs at temperatures below the amplitude fluctuation re-gime in the vicinity of the crossing point. For our analysis, we determine a temperature fitting range for each data set.…”

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

“…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].…”

Fluctuations aboveTcand the kinetic energy of Cooper pairs inLa1.9Sr0.1

“…We consider two kinds of scaling hypotheses: the first one based on fluctuation theory, [13][14][15][16][17][18][19] developed after the discovery of the high-T c superconductors, 20 as obtained by Ullah and Dorsey, 21 and by Rosenstein,18 who considered in different ways the effects of thermal fluctuations at the mean-field temperature T c ͑H͒. The second scaling law, also considered here, is purely phenomenological and based on a new temperature, T e ͑H͒.…”