High temperature superconductivity is often found in the vicinity of antiferromagnetism. This is also true in LaFeAsO1−xFx (x≤ 0.2) and many other iron-based superconductors, which leads to proposals that superconductivity is mediated by fluctuations associated with the nearby magnetism. Here we report the discovery of a new superconductivity dome without low-energy magnetic fluctuations in LaFeAsO1−xFx with 0.25≤x≤0.75, where the maximal critical temperature Tc at xopt = 0.5∼0.55 is even higher than that at x≤ 0.2. By nuclear magnetic resonance and Transmission Electron Microscopy, we show that a C4 rotation symmetry-breaking structural transition takes place for x> 0.5 above Tc. Our results point to a new paradigm of high temperature superconductivity.
@article{arxiv.1507.01750,
title = {New Superconductivity Dome in LaFeAsO$_{1-x}$F$_{x}$ Accompanied by Structural Transition},
author = {J. Yang and R. Zhou and L. L. Wei and H. X. Yang and J. Q. Li and Z. X. Zhao and Guo-qing Zheng},
journal= {arXiv preprint arXiv:1507.01750},
year = {2015}
}