Upper critical field and fluctuation conductivity in the critical regime of doped SmFeAsO

TL;DR

This study investigates the upper critical field and fluctuation conductivity in doped SmFeAsO, revealing a high field slope, two-dimensional fluctuation behavior, and coherence length variations with Tc, advancing understanding of its superconducting properties.

Contribution

The paper introduces a thermodynamic method to estimate the upper critical field slope from conductivity fluctuations, reducing criterion dependence in measurements.

Findings

High field slope of -12 T/K for optimally doped sample

Evidence of two-dimensional lowest Landau level scaling above 8 T

Coherence length increases as Tc decreases, confirming 2D superconductivity

Abstract

We measure magnetotransport of F doped SmFeAsO samples up to 28T and we extract the upper critical fields, using different criteria. In order to circumvent the problem of criterion-dependence Hc2 values, we suggest a thermodynamic estimation of the upper critical field slope dHc2/dT based on the analysis of conductivity fluctuations in the critical regime. A high field slope as large as -12T/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_0H_LLL=8T. Finally, we estimate the coherence length values and we observe that they progressively increase with decreasing Tc. 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.