Log-T divergence and Insulator-to-Metal Crossover in the normal state   resistivity of fluorine doped SmFeAsO1-xFx
  We report the resistivity of a series of fluorine-doped SmFeAsO1-xFx polycrystalline superconductors in magnetic fields up to 60T. For underdoped samples (x < 0.15), the low temperature resistive state is characterized by pronounced magneto-resistance and a resistive upturn at low temperatures. The "insulating behavior" is characterized by a log-T divergence observed over a decade in temperature. In contrast, the normal state for samples with doping x > 0.15 display metallic behavior with little magnetoresistance, where intense magnetic fields broaden the superconducting transition rather than suppress Tc. The location of the insulator-to metal crossover coincides with the reported suppression of the structural phase transition (SPT)in the phase diagram for SmFeAsO1-xFx series. 
S.C. Riggs, J.B. Kemper, Y. Jo, Z. Stegen, L. Balicas, G.S. Boebinger,   F.F. Balakirev, Albert Migliori, H. Chen, R. H. Liu...