title: Bulk superconductivity in bismuth oxysulfide Bi4O4S3.
abstract: A very recent report on the observation of superconductivity in Bi(4)O(4)S(3) [Mizuguchi, Y.; http://arxiv.org/abs/1207.3145] could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here the synthesis of Bi(4)O(4)S(3) at 500 °C by a vacuum encapsulation technique and its basic characterizations. The as-synthesized Bi(4)O(4)S(3) was contaminated with small amounts of Bi(2)S(3) and Bi impurities. The majority phase was found to be tetragonal (space group I4/mmm) with lattice parameters a = 3.9697(2) Å and c = 41.3520(1) Å. Both AC and DC magnetization measurements confirmed that Bi(4)O(4)S(3) is a bulk superconductor with a superconducting transition temperature (T(c)) of 4.4 K. Isothermal magnetization (M-H) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H(c1)) at 2 K for the new superconductor was found to be ~15 Oe. Magnetotransport measurements showed a broadening of the resistivity (ρ) and a decrease in T(c) (ρ = 0) with increasing magnetic field. The extrapolated upper critical field H(c2)(0) was ~31 kOe with a corresponding Ginzburg-Landau coherence length of ~100 Å . In the normal state, the ρ ~ T(2) dependence was not indicated. Hall resistivity data showed a nonlinear magnetic field dependence. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as-synthesized Bi(4)O(4)S(3). On the other hand, Bi heat-treated at the same temperature is not superconducting, thus excluding the possibility of impurity-driven superconductivity in the newly discovered superconductor Bi(4)O(4)S(3).
authors.affiliation: Quantum Phenomena and Applications Division, National Physical Laboratory (CSIR), Dr. K. S. Krishnan Road, New Delhi 110012, India.
authors.forename: Shiva Kumar
authors.initials: SK
authors.lastname: Singh
authors.forename: Anuj
authors.initials: A
authors.lastname: Kumar
authors.forename: Bhasker
authors.initials: B
authors.lastname: Gahtori
authors.lastname: Shruti
authors.forename: Gyaneshwar
authors.initials: G
authors.lastname: Sharma
authors.forename: Satyabrata
authors.initials: S
authors.lastname: Patnaik
authors.forename: Veer P S
authors.initials: VP
authors.lastname: Awana