Change in the electronic structure of the bismuth chalcogenide superconductor CsBi_4−xPb_xTe₆ by dissociation of the bismuth dimers

CsBi_4−xPb_xTe₆ is synthesized and the superconductivity associated with the structural transition from Pb substitution is studied. Photoemission spectroscopy measurements are performed in order to elucidate the relationship between the electronic structure and the occurrence of the superconductivity. When Bi is substituted with Pb, an electron doping-like change in the electronic structure is directly observed which is contrary to the naive expectation of hole doping. This observation is consistent with band structure calculations and appears to be a unique characteristic of CsBi_4−xPb_xTe₆ because of the dissociation of Bi dimers upon Pb substitution. These results indicate that it may be possible to control the electron and hole doping via manipulating the Bi dimers through Pb substitution. (paper)