Observation of anisotropic diamagnetism above the superconducting transition in iron pnictide Ba1−xKxFe

Abstract

High-resolution magnetization measurements performed in a high-quality Ba 1−x K x Fe 2 As 2 single crystal allowed to determine the diamagnetism induced above the superconducting transition by thermally activated Cooper pairs. These data, obtained with magnetic fields applied along and transverse to the crystal ab layers, demonstrate experimentally that the superconducting transition of iron pnictides may be explained at a phenomenological level in terms of the Gaussian Ginzburg-Landau approach for three-dimensional anisotropic superconductors.

Anisotropy dependence of the fluctuation spectroscopy in the critical and gaussian regimes in superconducting NaFe1−xCo x As single crystals

“…4(a), were performed with magnetic fields up to 5 T perpendicular to the ab layers, under zero-field-cooled (ZFC) and field-cooled (FC) conditions. As it may be seen in this figure, a rounding effect just below T c (which becomes more prominent upon increasing the applied magnetic field) and a broadening of the reversible region (where the ZFC and FC curves coincide) below T c , are substantial evidences of the fluctuation effects in the critical region, in agreement with recent results 13,14,16 . In this case the background contribution (which is mainly due to the crystal’s normal state) was determined by fitting a curie-like dependence m B ( T ) =  a  + b T  +  c / T to the as-measured m ( T ) H data in the temperature range from 25 K to 45 K (solid lines in Fig.…”

“…In the case of the x  = 0.03 crystal, the region where the 3D scaling is applicable is in excellent agreement with the prediction. The 3D scaling was also previously observed under similar field amplitudes in the fluctuation-induced magnetic susceptibility of a crystal of the same composition 16 , in single crystals of other iron-pnictide families 6,8,12,14,19,20 , and also in high- T c superconductors like optimally-doped YBa 2 Cu 3 O x 5,36 . In the case of the x  = 0.07 and 0.073 crystals the 3D-LLL scaling fails before reaching the Ginzburg criterion.…”

“…In Fig. 1(d–f) it is presented an example of the normal-state background extraction procedure, that consist in a linear fit above 1.5 T c , a temperature above which fluctuation effects are expected to be negligible 14,20,26 .

Figure 1( a – c ) Temperature dependence of resistivity near T c for NaFe 1− x Co x As ( x  = 0.03, 0.07, 0.073) crystals under different magnetic fields up to 8 T applied perpendicular to the crystals’ ab- planes. ( d – f ) Example (for µ 0 H  = 0 T) of the procedure used to determine the background contribution by a linear fit above 1.5 T c (lines).

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Diamagnetism above the superconducting transition in underdoped La1.9Sr0.1CuO4Mosqueira1, Dancausa2, Vidal3 2011Phys. Rev. B167290View full textAdd to dashboardCite

“…Another aspect that will need further examination on the grounds of our present results concerns the magnetization measurements above T c in iron pnictides, whereas detailed results in a high-quality Ba 1-x K x Fe 2 As 2 single crystal have been explained in terms of conventional GGL approaches, 40 recent measurements under very low-field amplitudes in a polycrystalline sample (SmFeAsO 0.8 F 0.2 ) present anomalies similar to the ones described here for LSCO samples. 41 …”

Effect of proton irradiation on the fluctuation-induced magnetoconductivity of FeSe1−xTexthin films

“…The analysis of fluctuation effects above the superconducting transition is an important way to obtain information about fundamental aspects of superconducting materials such as the critical magnetic fields, the coherence lengths, the anisotropy, or the dimensionality (at present a highly debated issue in iron-based superconductors, see [17][18][19][20][21][22][23][24][25]. In these materials the Ginzburg number (which is associated with the width of the critical fluctuations region around T c ) is half that of conventional low-T c superconductors and high-T c cuprates, so fluctuation effects are expected to play an important role [17].…”