Probing multi-band superconductivity and magnetism in   SmFeAsO$_{0.8}$F$_{0.2}$ single crystals by high-field vortex torque   magnetometry
  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. 
L. Balicas, A. Gurevich, Y. J. Jo, J. Jaroszynski, D. C. Larbalestier,   R. H. Liu, H. Chen, X. H. Chen, N. D. Zhigadlo, S. ...