Signature of multigap nodeless superconductivity in fluorine-doped NdFeAsO

Abstract

We investigate the temperature dependence of the lower critical field $H_{c1}(T)$, the field at which vortices penetrate into the sample, of a high-quality fluorine-doped NdFeAsO single crystal under static magnetic fields $H$ parallel to the $c$-axis. The temperature dependence of the first vortex penetration field has been experimentally obtained and pronounced changes of the $H_{c1}$(T) curvature are observed, which is attributed to the multiband superconductivity. Using a two-band model with $s$-wave-like gaps, the temperature-dependence of the lower critical field $H_{c1}(T)$ can be well described. These observations clearly show that the superconducting energy gap in fluorine-doped NdFeAsO is nodeless. The values of the penetration depth at $T$ = 0\,K have been determined and confirm that the pnictide superconductors obey an Uemura-style relationship between $T_c$ and ${\lambda }_{ab}(0{)}^{-2}$

7 pages, 4 figures

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• Self-consistent two-gap approach in studying multi-band superconductivity in NdFeAsO${}_{0.65}$F${}_{0.35}$
• Data analysis of $ab$ $initio$ effective Hamiltonians in iron-based superconductors $\unicode{x2014}$ Construction of predictors for superconducting critical temperature
• Grain boundary characteristics of oxypnictide NdFeAs(O,F) superconductors