1202.5367 (N. Fujiwara et al.)

^{75}As NMR study of the growth of paramagnetic-metal domains due to
electron doping near the superconducting phase in LaFeAsO_{1-x}F_{x}    [PDF]

N. Fujiwara, T. Nakano, Y. Kamihara, H. Hosono

We studied the electric and magnetic behavior near the phase boundary between
antiferromagnetic (AF) and superconducting (SC) phases for a prototype of
high-T_c pnictides LaFeAsO_{1-x}F_{x} by using nuclear magnetic resonance, and
found that paramagnetic-metal (PM) domains segregate from AF domains. PM
domains grow in size with increasing electron doping level and are accompanied
by the onset of superconductivity, and thus application of pressure or
increasing the doping level causes superconductivity. The existence of PM
domains cannot be explained by the existing paradigm that focuses only on the
relationship between superconductivity and antiferromagnetism. Based on orbital
fluctuation theory, the existence of PM domains is evidence of the
ferroquadrupole state.

View original: http://arxiv.org/abs/1202.5367