Probing multi-band superconductivity and magnetism in SmFeAsO${}_{0.8}$F${}_{0.2}$ single crystals by high-field vortex torque magnetometry

Abstract

To probe manifestations of multiband superconductivity in oxypnictides, we measured the angular dependence of magnetic torque $\tau (\theta )$ in the mixed state of SmO${}_{0.8}$F${}_{0.2}$FeAs single crystals as functions of temperature $T$ and high magnetic field $H$ up to 30 T. We show that the effective mass anisotropy parameter $\gamma$ extracted from $\tau (\theta )$, can be greatly overestimated if the strong paramagnetism of Sm or Fe ions is not properly taken into account. The correctly extracted $\gamma$ depends on both $T$ and $H$, saturating at $\gamma \simeq 9$ at lower temperatures. Neither the London penetration depth nor the superfluid density is affected by high fields fields up to the upper critical field. Our results indicate two strongly-coupled superconducting gaps of nearly equal magnitudes.

arXiv comment5 pages, 5 figures

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