Systematic study of electronic states of Ln(O,F)BiS2 by spin- and angle-resolved photoemission spectroscopy

The evolution of fine electronic structures in superconducting LnO1-xFxBiS2 (Ln denotes lanthanoid) is systematically investigated with spin- and angle-resolved photoemission spectroscopy. A shape change of the Fermi surface (FS) at the X point from elliptical to rectangular with increasing the electron doping is commonly observed in different lanthanide systems. Besides that, an emergent large Fermi surface around the CYRILLIC CAPITAL LETTER GHE point is also observed in all the samples with different doping levels deviating from the theoretical prediction, which might be related to the superconductivity. In addition, we found a humped band around X(ir,0) in the highly doped samples only, which may be attributed to the BiS2 surface reconstruction or surface defects relying on the electron concentration. We also demonstrate the spin-selective excitation of photoelectrons, which indicates the presence of spin-orbital-entangled bulk Rashba splitting in this system. This result may enable the optical tuning of electron spin in a BiS2-based system.