Strongly three-dimensional electronic structure and Fermi surfaces ofSrFe2(As0.65P0.35)2: Comparison withBaFe2(As1−xPx)2

Abstract

The isovalent-substituted iron-pnictide superconductor ${\mathrm{SrFe}}_{2}$(${\mathrm{As}}_{1\text{\ensuremath{-}}x}$${\mathrm{P}}_{x}$)${}_{2}$ ($x=0.35$) has a slightly higher optimum critical temperature than the similar system ${\mathrm{BaFe}}_{2}$(${\mathrm{As}}_{1\text{\ensuremath{-}}x}$${\mathrm{P}}_{x}$)${}_{2}$, and its parent compound ${\mathrm{SrFe}}_{2}$${\mathrm{As}}_{2}$ has a much higher N\'eel temperature than ${\mathrm{BaFe}}_{2}$${\mathrm{As}}_{2}$. We have studied the band structure and the Fermi surfaces of optimally doped ${\mathrm{SrFe}}_{2}$(${\mathrm{As}}_{1\text{\ensuremath{-}}x}$${\mathrm{P}}_{x}$)${}_{2}$ by angle-resolved photoemission spectroscopy (ARPES). Three holelike Fermi surfaces (FSs) around $(0,0)$ and two electronlike FSs around $(\ensuremath{\pi},\ensuremath{\pi})$ have been observed as in the case of ${\mathrm{BaFe}}_{2}$(${\mathrm{As}}_{1\text{\ensuremath{-}}x}$${\mathrm{P}}_{x}$)${}_{2}$. Measurements with different photon energies have revealed that the outermost hole FS is more strongly warped along the ${k}_{z}$ direction than the corresponding one in BaFe(${\mathrm{As}}_{1\text{\ensuremath{-}}x}$${\mathrm{P}}_{x}$)${}_{2}$, and that the innermost one is an ellipsoidal pocket. The electron FSs are almost cylindrical, unlike the corrugated ones in BaFe(${\mathrm{As}}_{1\text{\ensuremath{-}}x}$${\mathrm{P}}_{x}$)${}_{2}$. A comparison of the ARPES data with a first-principles band-structure calculation revealed that the quasiparticle mass renormalization factors are different not only between bands of different orbital character, but also between the hole and electron FSs of the same orbital character. By examining the nesting conditions between the hole and electron FSs, we conclude that magnetic interactions between FeAs layers rather than FS nesting play an important role in stabilizing the antiferromagnetic order. The insensitivity of superconductivity to the FS nesting can be explained if only the ${d}_{xy}$ and/or ${d}_{xz/yz}$ orbitals are active in inducing superconductivity or if FS nesting is not important for superconductivity.