Evaluation of Bi defect concentration in LnO_1-xF_xBiCh₂ by scanning tunneling microscopy

We examined a concentration of Bi defects in layered BiCh₂ based superconductors LnO_1-xF_xBiCh₂ (Ln = La, Ce, Nd Ch = S, Se). These materials show superconductivity by electron carrier doping into BiCh₂ layer. Since Bi defects affect the carrier concentration directly, an examination of the concentration is important to evaluate an actual carrier concentration. In this paper, the concentration of Bi defects on the BiCh₂ layers in BiCh₂ based superconductors was evaluated by scanning tunneling microscopy measurements in real space. We found the samples with BiSe₂ layers have less Bi defects than those with BiS₂ layers. Furthermore, the concentration of Bi defects was found to be almost constant regardless of F concentration and Ln ion.