Istituto dei materiali per l'elettronica ed il magnetismo     
Pallecchi I., Fanciulli C., Tropeano M., Palenzona A., Ferretti M., Malagoli A., Martinelli A., Sheikin I., Putti M., Ferdeghini C. Upper critical field and fluctuation conductivity in the critical regime of doped SmFeAsO. In: Physical Review B, vol. 79 article n. 104515. The American Physical Society, 2009.
We measure magnetotransport of F-doped SmFeAsO samples up to 28 T and we extract the upper critical fields, using different criteria. In order to circumvent the problem of criterion-dependent H-c2 values, we suggest a thermodynamic estimation of the upper critical field slope dH(c2)/dT based on the analysis of conductivity fluctuations in the critical regime. A high field slope as large as -12 T/K is thus extracted for the optimally doped sample. We find evidence of a two-dimensional lowest Landau level (LLL) scaling for applied fields larger than mu H-0(LLL)similar to 8 T. Finally, we estimate the coherence length values and we observe that they progressively increase with decreasing T-c. In all cases, the coherence length values along the c axis are smaller than the interplanar distance, confirming the two-dimensional nature of superconductivity in this compound.
URL: http://link.aps.org/doi/10.1103/PhysRevB.79.104515
DOI: 10.1103/PhysRevB.79.104515
Subject 74.40.+k

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