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Very recent report 1 on observation of superconductivity in Bi 4 O 4 S 3 could potentially reignite the search for superconductivity in a broad range of layered sulfides. We report here synthesis of Bi 4 O 4 S 3 at 500 0 C by vacuum encapsulation technique and its basic characterizations. Bi 4 O 4 S 3 is contaminated by small amounts of Bi 2 S 3 and Bi impurities. The majority phase is tetragonal I4/mmm space group with lattice parameters a = 3.9697(2)Å, c = 41.3520(1)Å. Both AC and DC magnetization measurements confirmed that Bi 4 O 4 S 3 is a bulk superconductor with superconducting transition temperature (T c ) of 4.4K. Isothermal magnetization (MH) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (H c1 ) at 2K, of the new superconductor is found to be ~15 Oe. The magneto-transport R(T, H) measurements showed a resistive broadening and decrease in T c (ρ=0) to lower temperatures with increasing magnetic field. The extrapolated upper critical field H c2 (0) is ~ 31kOe with a corresponding Ginzburg-Landau coherence length of ~100Å . In the normal state the ρ ~ T 2 is not indicated. Hall resistivity data show non-linear 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 same temperature heat treated Bi is not superconducting, thus excluding possibility of impurity driven superconductivity in the newly discovered Bi 4 O 4 S 3 superconductor.

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We report appearance of superconductivity at 5 K in NdO0.5F0.5BiS2 and supplement the discovery [Demura et al., e-print arXiv:1207.5248] of the same in layered sulfide based compound. Detailed structural analysis showed that the studied compound is crystallized in tetragonal P4/nmm space group with lattice parameters a = 3.9911(3) Å and c = 13.3830(2) Å. Bulk superconductivity is established in NdO0.5F0.5BiS2 at 5 K by both transport and magnetic measurements. Electrical transport measurements showed superconducting Tc onset at 5.2 K and Tc (ρ = 0) at 4.7 K. Under applied magnetic field, both Tc onset and Tc (ρ = 0) decrease to lower temperatures and an upper critical field [Hc2(0)] of above 23 kOe is estimated. Isothermal magnetization exhibited typical type-II behavior with lower critical field (Hc1) of around 25 Oe. Specific heat [Cp(T)] is investigated in the temperature range of 1.9–50 K in zero external magnetic field. A Schottky-type anomaly is observed at low temperature below 7 K.

Abstract-In this work, we study a fundamental tradeoff issue in designing distributed hash ). They asked whether this represents the best asymptotic "state-efficiency" tradeoffs. Our first major result is to show that there are straightforward routing algorithms which achieve better asymptotic tradeoffs. However, such algorithms all cause severe congestion on certain network nodes, which is undesirable in a P2P network. We then rigorously define the notion of "congestion" and conjecture that the above tradeoffs are asymptotically optimal for a congestion-free network. In studying this conjecture, we have thoroughly clarified the role that "congestionfree" plays in this "state-efficiency" tradeoff. Our second major result is to prove that the aforementioned tradeoffs are asymptotically optimal for uniform algorithms. Furthermore, for uniform algorithms, we find that the routing table size of Ω(log2n) is a magic threshold point that separates two different "state-efficiency" regions. Our third and final result is to study the exact (instead of asymptotic) optimal tradeoffs for uniform algorithms. We propose a new routing algorithm that reduces the routing table size and the network diameter of Chord both by 21.4% without introducing any other protocol overhead, based on a novel number-theoretical technique.