Abstract
The competition of magnetic order and superconductivity is a key element in the physics of all unconventional superconductors, for example in high-transition-temperature cuprates1, heavy fermions2 and organic superconductors3. Here superconductivity is often found close to a quantum critical point where long-range antiferromagnetic order is gradually suppressed as a function of a control parameter, for example charge-carrier doping or pressure. It is believed that dynamic spin fluctuations associated with this quantum critical behaviour are crucial for the mechanism of superconductivity. Recently, high-temperature superconductivity has been discovered in iron pnictides, providing a new class of unconventional superconductors4,5,6. Similar to other unconventional superconductors, the parent compounds of the pnictides show a magnetic ground state7,8 and superconductivity is induced on charge-carrier doping. In this Letter the structural and electronic phase diagram is investigated by means of X-ray scattering, muon spin relaxation and Mössbauer spectroscopy on the series LaO1−xFxFeAs. We find a discontinuous first-order-like change of the Néel temperature, the superconducting transition temperature and the respective order parameters. Our results strongly question the relevance of quantum critical behaviour in iron pnictides and prove a strong coupling of the structural orthorhombic distortion and the magnetic order both disappearing at the phase boundary to the superconducting state.
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Acknowledgements
The work at the IFW Dresden and at Cologne University has been supported by the DFG through FOR 538 and SFB 608, respectively.
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Luetkens, H., Klauss, HH., Kraken, M. et al. The electronic phase diagram of the LaO1−xFxFeAs superconductor. Nature Mater 8, 305–309 (2009). https://doi.org/10.1038/nmat2397
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DOI: https://doi.org/10.1038/nmat2397
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