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Nanoscale Charge Segregation in Underdoped 1111 Iron Pnictides

Using nuclear resonance measurements, we examine the doping dependence of the charge distribution in fluorine-doped La-111 samples. In the optimally-doped and overdoped regions, an homogeneous charge distribution is observed. On the contrary, for dopings right above the boundary between long-range ordered magnetism and superconductivity, i.e. in the underdoped region, the charge distribution is found to be inhomogeneous. We show that this occurs at the nanoscale and argue that this spatial variation reflects intrinsic local differences in doping, with low and high doping regions. These two sets of regions feature identical critical temperatures, suggesting that the high doping regions support superconductivity in the low doping regions which are otherwise more magnetically-correlated. We argue that this nanoscale charge segregation reconciles the various proposed phase diagrams.

NQR; iron pnictides; superconductivity

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