Suppression of superconductivity in layered Bi4O4S3 by Ag doping
  We report X-ray diffraction, magnetization and transport measurements for polycrystalline samples of the new layered superconductor Bi4-xAgxO4S3 (0<x<0.2). The superconducting transition temperature (TC) decreases gradually and finally suppressed for x>0.10. Accordingly, the resistivity changes from a metallic behavior for x<0.1 to a semiconductor-like behavior for x>0.1. The analysis of Seebeck coefficient shows there are two types of electron-like carriers dominate at different temperature regions, indicative of a multiband effect responsible for the transport properties. The suppression of superconductivity and the increased resistivity can be attributed to a shift of the Fermi level to the lower-energy side upon doping, which reduces the density of states at EF. Further, our result indicates the superconductivity in the parent Bi4O4S3 is intrinsic and the dopant Ag prefers to enter the BiS2 layers, which may essentially modify the electronic structure. 
S. G. Tan, P. Tong, Y. Liu, W. J. Lu, L. J. Li, B. C. Zhao, Y. P. Sun
cond-mat.supr-con cond-mat.mtrl-sci