Electronic Structure of Sr <sub/>1?</sub><i> <sub/>y</sub></i> Ca <i> <sub/>y</sub></i> Fe <sub/>2</sub> (As <sub/>1?</sub><i> <sub/>x</sub></i> P <i> <sub/>x</sub></i> ) <sub/>2</sub> ( <i>x</i> = 0.25, <i>y</i> = 0.08) Revealed by Angle-Resolved Photoemission Spectroscopy

摘要： We have investigated the electronic structure of Sr1?yCayFe2(As1?xPx)2 (x = 0.25, y = 0.08) by means of angle-resolved photoemission spectroscopy. From the comparison with the results of BaFe2(As1?xPx)2, the effects of smaller structural anisotropy (c/a) on the Fermi surfaces (FSs) and the gap structures are discussed. The observed FSs have three dimensional shapes. One of the hole FSs is strongly warped between the Γ and Z points, and the innermost FS observed at the Z point disappears at the Γ point, which is similar to the FS features of SrFe2(As1?xPx)2 (x = 0.35). In the superconducting state, the node like gap-minimum is present for the dxy electron FS near the X point, while the gaps around the other high symmetry points are isotropic. Several theoretical models based on the spin and/or the orbital fluctuation are examined to explain all these experimental results.