Electronic Structure of ${\mathrm{S}\mathrm{r}}_{1-y}{\mathrm{C}\mathrm{a}}_y\mathrm{F}{\mathrm{e}}_2({\mathrm{A}\mathrm{s}}_{1-x}{\mathrm{P}}_x{)}_2$ ($x$ = 0.25, $y$ = 0.08) Revealed by Angle-Resolved Photoemission Spectroscopy

We have investigated the electronic structure of ${\mathrm{S}\mathrm{r}}_{1-y}{\mathrm{C}\mathrm{a}}_y\mathrm{F}{\mathrm{e}}_2({\mathrm{A}\mathrm{s}}_{1-x}{\mathrm{P}}_x{)}_2$ ($x$ = 0.25, $y$ = 0.08) by means of angle-resolved photoemission spectroscopy. From the comparison with the results of $\mathrm{B}\mathrm{a}\mathrm{F}{\mathrm{e}}_2({\mathrm{A}\mathrm{s}}_{1-x}{\mathrm{P}}_x{)}_2$, the effects of smaller structural anisotropy ($c\mathrm{/}a$) 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 $\mathrm{\Gamma }$ and $Z$ points, and the innermost FS observed at the $Z$ point disappears at the $\mathrm{\Gamma }$ point, which is similar to the FS features of $\mathrm{S}\mathrm{r}\mathrm{F}{\mathrm{e}}_2({\mathrm{A}\mathrm{s}}_{1-x}{\mathrm{P}}_x{)}_2$ ($x$ = 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.