Electronic structure of self-doped layered Eu3 F4Bi2 S4 material revealed by x-ray absorption spectroscopy and photoelectron spectromicroscopy

We have studied the electronic structure of ${\mathrm{Eu}}_{3}{\mathrm{F}}_{4}{\mathrm{Bi}}_{2}{\mathrm{S}}_{4}$ using a combination of Eu ${L}_{3}$-edge x-ray absorption spectroscopy (XAS) and space-resolved angle-resolved photoemission spectroscopy (ARPES). From the Eu ${L}_{3}$-edge XAS, we have found that the Eu in this system is in mixed valence state with coexistence of ${\mathrm{Eu}}^{2+}/{\mathrm{Eu}}^{3+}$. The bulk charge doping was estimated to be $\ensuremath{\sim}0.3$ per Bi site in ${\mathrm{Eu}}_{3}{\mathrm{F}}_{4}{\mathrm{Bi}}_{2}{\mathrm{S}}_{4}$, which corresponds to the nominal $x$ in a typical RE${\mathrm{O}}_{1\ensuremath{-}x}{\mathrm{F}}_{x}{\mathrm{BiS}}_{2}$ system (RE: rare-earth elements). From the space-resolved ARPES, we have ruled out the possibility of any microscale phase separation of Eu valence in the system. Using a microfocused beam we have observed the band structure as well as the Fermi surface that appeared similar to other compounds of this family with disconnected rectangular electronlike pockets around the $X$ point. The Luttinger volume analysis gives the effective carrier to be 0.23 electrons per Bi site in ${\mathrm{Eu}}_{3}{\mathrm{F}}_{4}{\mathrm{Bi}}_{2}{\mathrm{S}}_{4}$, indicating that the system is likely to be in the underdoped region of its superconducting phase diagram.