Electronic Structure of Sr_1−yCa_yFe₂(As_1−xP_x)₂ (x = 0.25, y = 0.08) Revealed by Angle-Resolved Photoemission Spectroscopy

Abstract

We have investigated the electronic structure of Sr 1−y Ca y Fe 2 (As 1−x P x ) 2 (x = 0.25, y = 0.08) by means of angle-resolved photoemission spectroscopy. From the comparison with the results of BaFe 2 (As 1−x P x ) 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 SrFe 2 (As 1−x P x ) 2 (x = 0.35). In the superconducting state, the node like gap-minimum is present for the d xy 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.