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 Eu3F4Bi2S4 using a combination of Eu L3-edge x-ray absorption spectroscopy (XAS) and space-resolved angle-resolved photoemission spectroscopy (ARPES). From the Eu L3-edge XAS, we have found that the Eu in this system is in mixed valence state with coexistence of Eu2+/Eu3+. The bulk charge doping was estimated to be ∼0.3 per Bi site in Eu3F4Bi2S4, which corresponds to the nominal x in a typical REO1−xFxBiS2 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 Eu3F4Bi2S4, indicating that the system is likely to be in the underdoped region of its superconducting phase diagram.