Electronic ground states and phase diagrams of Fe-pnictide superconductors

过渡金属化合物的电子相图表现出超导性和磁性的复杂相互作用。过渡金属的低矩磁自旋密度波（SDW）有序存在于以不同费米表面上不同能隙共存为特征的多带超导旁。在稀土元素存在的情况下，发现了独立的稀土磁有序相以及稀土-过渡金属磁有序相的相互作用。利用局域探针μSR （μ on spin relaxation）和Mössbauer光谱，我们测定了标记为011、122、1111和22426的铁nicides和chalgogenides的电子基态和相图。我们独立地确定了磁性和超导序参量以及它们各自的体积分数作为载流子掺杂、磁场和外部压力的函数。在第二个资助期特别感兴趣的是超导和磁有序微观共存的系统。在掺杂的122fe化合物中发现了各自序参量的直接相互作用。应该详细研究这种相互作用，以揭示潜在的微观机制。在铁基超导体中，几种不同的取代策略导致了超导性，即在电子活性铁镍或硫系平面上取代单价或三价元素在A位上或在铁位上取代不同的过渡金属。除了载流子掺杂机制外，散射势也有很大的不同。应研究这如何影响电子基态相的性质。在1111体系中，我们计划研究通过高压合成制备的新样品，预期这些样品具有更好的均匀性和生长单晶的可能性。

The electronic phase diagrams of transition metal pnictides exibit a complex interplay of superconductivity and magnetism. Low moment magnetic spin density wave (SDW) ordering of the transition metal is found next to multi-band superconductivity characterized by a coexistence of different energy gaps on different Fermi surface sheets. In the presence of rare earth elements independent rare earth magnetic ordering is found as well as interacting rare earth – transition metal magnetically ordered phases. Using the local probes muon spin relaxation (μSR) and Mössbauer spectroscopy we determine the electronic ground states and the phase diagram in iron pnictides and chalgogenides with increasing interlayer distance, labeled 011, 122, 1111, and 22426. We determine independently the magnetic and superconducting order parameters and their respective volume fractions as a function of charge carrier doping, magnetic field and external pressure. Of particular interest in the second funding period are systems where a microscopic coexistence of superconductivity and magnetic order is found. In doped 122 Fe pnictides a direct interplay of the respective order parameters is found. This interplay shall be studied in detail to reveal the underlying microscopic mechanisms. In the iron-based superconductors several different substitution strategies lead to superconductivity, i.e. substituting mono or trivalent elements on the A site or different transition metals on the Fe-site in the electronically active Fe pnictide or chalgogenide planes. Besides charge carrier doping mechanisms also the scattering potentials are very different. It shall be investigated how this influences the properties of the electronic ground state phases. In 1111 systems we plan to examine new samples prepared by high pressure synthesis for which a better homogeneity and the possibility to grow single crystals is anticipated.