We report the Hall resistivity, ρxy of polycrystalline SmFeAsO1−xFx for four different fluorine concentrations from the onset of superconductivity through the collapse of the structural phase transition. For the two more highly-doped samples, ρxy is linear in magnetic field up to 50 T with only weak temperature dependence, reminiscent of a simple Fermi liquid. For the lightly-doped samples with x<0.15, we find a low temperature regime characterized ρxy(H) being both non-linear in magnetic field and strongly temperature dependent even though the Hall angle is small. The onset temperature for this non-linear regime is in the vicinity of the structural phase (SPT)/spin density wave (SDW) transitions. The temperature dependence of the Hall resistivity is consistent with a thermal activation of carriers across an energy gap. The evolution of the energy gap with doping is reported.
@article{arxiv.0809.2820,
title = {Doping-Driven Collapse of the SDW Correlation Gap in SmFeAsO$_{1-x}$F$_{x}$},
author = {Scott C. Riggs and R. D. McDonald and J. B. Kemper and Z. Stegen and G. S. Boebinger and F. F. Balakirev and Y. Kohama and A. Migliori and H. Chen and R. H. Liu and X. H. Chen},
journal= {arXiv preprint arXiv:0809.2820},
year = {2008}
}