Electronic origin of structural transition in 122 Fe based superconductors

Abstract

Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies E dxz , E dyz of Fe at the high symmetry points of the Brillouin zone. The fractional co-ordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.

Stoner factors of doped 122 Fe-based superconductors: First principles results

“…It should also be noted that the c-axis increases with the increasing doping concentration for both Na and K doping (in case of Na doped Ba122 materials c-axis increases with doping up to certain doping concentration and after that it decreases). This qualitatively explains the observed behaviour of z As with doping for K and Na doped Ba122 systems [55]. But in both the cases Fe-As bond length decreases with increasing doping concentration.…”

Spin-Orbital-Intertwined Nematic State in FeSe

“…Furthermore, we also plot the temperature dependent orthorhombic distortion of the lattice δ(T ) in Fig. 3(a), which is proportional to ∆ o (T ) [59]. Neither ∆ 77 K(T ) nor ∆ 57 K(T ) could be scaled to δ(T ).…”

Recent progress in NMR studies on high-<italic>T</italic><sub>c</sub> superconductors

“…为了进一步探究在铁基超导体中SOC效应及其对 电子向列相的影响, Li等人 [135] 在合成的高丰度(>98%) 0 K开始降低, 这在之前的NMR实验中有被观测到, 但是仍不清楚其起源 [97,141] . 其次, 在图39(a)中作出了 与轨道序参量∆ o (T)严格成正比的晶格正交畸变度 δ(T) [142] .…”