Luetkens H, Klauss H-H, Kraken M, Litterst F J, Dellmann T, Klingeler R, Hess C, Khasanov R, Amato A, Baines C, Kosmala M, Schumann O J, Braden M, Hamann-Borrero J, Leps N, Kondrat A, Behr G, Werner J, Büchner B
Laboratory for Muon-Spin Spectroscopy, Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland.
Nat Mater. 2009 Apr;8(4):305-9. doi: 10.1038/nmat2397. Epub 2009 Feb 22.
The competition of magnetic order and superconductivity is a key element in the physics of all unconventional superconductors, for example in high-transition-temperature cuprates, heavy fermions and organic superconductors. 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 superconductors. Similar to other unconventional superconductors, the parent compounds of the pnictides show a magnetic ground state 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 LaO(1-x)F(x)FeAs. 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.
磁有序与超导性之间的竞争是所有非常规超导体物理学中的关键要素，例如在高温转变温度铜酸盐、重费米子和有机超导体中。在这里，超导性常常出现在接近量子临界点的地方，在该点，长程反铁磁序会随着一个控制参数（例如载流子掺杂或压力）的变化而逐渐被抑制。据信，与这种量子临界行为相关的动态自旋涨落对于超导机制至关重要。最近，在铁基磷化物中发现了高温超导性，这提供了一类新的非常规超导体。与其他非常规超导体类似，磷化物的母体化合物呈现出磁基态，并且在载流子掺杂时会诱导出超导性。在本信函中，通过对系列LaO(1 - x)F(x)FeAs进行X射线散射、μ子自旋弛豫和穆斯堡尔谱研究了其结构和电子相图。我们发现奈尔温度、超导转变温度以及各自的序参量发生了类似一级的不连续变化。我们的结果强烈质疑了铁基磷化物中量子临界行为的相关性，并证明了结构正交畸变与磁有序之间的强耦合在与超导态的相界处均消失。
