Superconductivity in Bismuth Oxysulfide Bi

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Bismuth oxysulfide Bi<inf>4</inf>O<inf>4</inf>S<inf>3</inf>, which has recently been claimed to be an exotic superconductor (T_{\text{c}} = 4.5 K), was investigated by magnetic susceptibility and electrical resistivity measurements as well as by electron probe microanalysis. Single-phase Bi<inf>4</inf>O<inf>4</inf>S<inf>3</inf>was successfully prepared by a high-pressure method, and its lattice parameters and normal-state resistivity, as well as the density of states at the Fermi level, were found to be comparable to those determined earlier. However, the observed superconductivity was most likely impurity-driven, strictly contradictory to the observations in ongoing experiments. The present results indicate that the superconductivity of Bi<inf>4</inf>O<inf>4</inf>S<inf>3</inf>does not truly reflect the bulk nature of the BiS<inf>2</inf>layered phase, regardless of the manner in which Bi<inf>4</inf>O<inf>4</inf>S<inf>3</inf>is synthesized. We discuss possible superconducting impurities.
2013-07-15