Diamagnetic fluctuations inYBa2Cu3O7−xand

Abstract

We report on isofield curves of ͱ −M vs T, where M is the reversible magnetization, of YBa 2 Cu 3 O 6.95 , YBa 2 Cu 3 O 6.65 , and Bi 2 Sr 2 CaCu 2 O 8+x with the magnetic field, H, applied parallel to the c axis of the samples ͑and also parallel to the ab planes for YBaCuO͒. For temperatures close to the critical temperature, T c , the quantity ͱ −M is proportional to the order parameter amplitude ͉͉. Curves of ͱ −M vs T allowed to study the asymptotic behavior of the form ͑T a − T͒ m of ͉͉ near T c , as a function of field. Results for the studied samples produced values of T a ͑H͒ lying above T c , suggesting that the magnetic field gradually allows to probe a region of temperatures where phase correlations persist above T c . The study performed here in YBaCuO samples allowed to study how phase correlations evolve with doping in the pseudogap region of YBaCuO. ͱ −M vs T curves for all samples show a rather large amplitude fluctuation with no phase correlation extending well above T a ͑H͒ which is interpreted in terms of a Gaussian Ginzburg-Landau approach with a total-energy cutoff in the fluctuation spectrum. Resulting values for the exponent m found for all samples, 0.5Ͻ m Ͻ 0.7, are interpreted as due to phase fluctuations of the d-wave pairing symmetry of the order parameter in the ab planes.

Study of Nb0.18Re0.82non-centrosymmetric superconductor in the normal and superconducting states

“…Consequently, the exponent m may differ significantly from the mean-field value, as observed in the non-centrosymmetric Li 2 (Pd-Pt) 3 B superconductor [44]. where, T a (H) is the apparent transition temperature and m is the fitting exponent [44][45][46]. Deviation of m from the mean field value (m = 1/2), suggests the phase-mediated transition.…”

Strong thermal fluctuations in cuprate superconductors in magnetic fields aboveTc

“…were measured in many high-T c cuprate [41][42][43] and explained within the lowest Landau level approximation [45,46] valid for ε b. It turns out that an addition requirement for the intersection point is εd 2 1.…”

Non-conventional superconducting fluctuations in Ba(Fe1−xRhx)2As2 iron-based superconductors

“…We note that superconducting fluctuations in iron-based superconductors have been recently studied also by magnetoconductivity and magnetization, in the high field limit. [23][24][25] In these cases, the critical fluctuation region has a three dimensional nature. We show that our results, at high field, agree with the literature, while the low field limit results, not yet studied on these compounds, can be explained in terms of non GL fluctuations.…”