Direct observation of the influence of the As-Fe-As angle on the Tc of   superconducting SmFeAsO$_{1-x}$F$_{x}$
  The electrical resistivity, crystalline structure and electronic properties calculated from the experimentally measured atomic positions of the compound SmFeAsO$_{0.81}$F$_{0.19}$ have been studied up to pressures ~20GPa. The correlation between the pressure dependence of the superconducting transition temperature (Tc) and crystallographic parameters on the same sample shows clearly that a regular FeAs$_{4}$ tetrahedron maximizes Tc, through optimization of carrier transfer to the FeAs planes as indicated by the evolution of the electronic band structures. 
G. Garbarino, R. Weht, A. Sow, A. Sulpice, P. Toulemonde, M.   \'Alvarez-Murga, P. Strobel, P. Bouvier, M. Mezouar, M. N\'u\...
cond-mat.supr-con