Synthesis and superconductivity of new BiS2 based superconductor PrO0.5F0.5BiS2

We report synthesis and superconductivity at 3.7K in PrO0.5F0.5BiS2. The newly discovered material belongs to the layered sulfide based REO0.5F0.5BiS2 compounds having ZrCuSiAs type structure. The bulk polycrystalline compound is synthesized by vacuum encapsulation technique at 7800C in single step. Detailed structural analysis has shown that the as synthesized PrO0.5F0.5BiS2 is crystallized in tetragonal P4/nmm space group with lattice parameters a = 4.015(5) {\AA}, c = 13.362(4) {\AA}. Bulk superconductivity is observed in PrO0.5F0.5BiS2 below 4K from magnetic and transport measurements. Electrical transport measurements showed superconducting transition temperature (Tc) onset at 3.7K and Tc ({\rho}=0) at 3.1K. Hump at Tc related to superconducting transition is not observed in heat capacity measurement and rather a Schottky-type anomaly is observed at below ~6K. The compound is slightly semiconducting in normal state. Isothermal magnetization (MH) exhibited typical type II behavior with lower critical field (Hc1) of around 8Oe.Comment: Short note 10 pages text+figs. First report on PrO.5F.5BiS2 Su

Crossing point phenomena (T* = 2.7 K) in specific heat curves of superconducting ferromagnets RuSr2Gd1.4Ce0.6Cu2O10-{\delta}

Crossing point phenomena are one of the interesting and still puzzling effects in strongly correlated electron systems. We have synthesized RuSr2Gd1.4Ce0.6Cu2O10-{\delta} (GdRu-1222) magneto-superconductor through standard solid state reaction route and measured its magnetic, transport and thermal properties. We also synthesized RuSr2Eu1.4Ce0.6Cu2O10-{\delta} (EuRu-1222) then measured its heat capacity in zero magnetic fields for reference. The studied compounds crystallized in tetragonal structure with space group I4/mmm. GdRu-1222 is a reported magneto-superconductor with Ru spins magnetic ordering at temperature around 110 K and superconductivity in Cu-O2 planes below around 40 K. To explore the crossing point phenomena, the specific heat [Cp (T)] was investigated in temperature range 1.9-250 K, under magnetic field of up to 70 kOe. Unfortunately though no magnetic and superconducting transitions are observed in specific heat, a Schottky type anomaly is observed at low temperatures below 20 K. This low temperature Schottky type anomaly can be attributed to splitting of the ground state spectroscopic term 8S7/2 of paramagnetic Gd3+ ions by both internal and external magnetic fields. It was also observed that Cp (T) being measured for different values of magnetic field, possesses the same crossing point (T* = 2.7 K), up to the applied magnetic field 70 kOe. A quantitative explanation of this phenomenon, based on its shape and temperature dependence of the associated generalized heat capacity (Cp), is presented. This effect supports the crossing point phenomena, which is supposed to be inherent for strongly correlated systems.Comment: 12 pages Text+Figs ([email protected]

Soft Carrier Multiplications by Hot Electrons in Graphene

By using Boltzmann formalism, we show that carrier multiplication by impact ionization can take place at relatively low electric fields during electronic transport in graphene. Because of the absence of energy gap, this effect is not characterized by a field threshold unlike in conventional semiconductors, but is a quadratic function of the electric field. We also show that the resulting current is an increasing function of the electronic temperature, but decreases with increasing carrier concentration

Superconductivity at 5K in NdO0.5F0.5BiS2

We report appearance of superconductivity at 5K in NdO0.5F0.5BiS2 and supplement the discovery [1] of the same in layered sulfide based ZrCuSiAs type compounds. The bulk polycrystalline compound is synthesized by conventional solid state route via vacuum encapsulation technique. Detailed structural analysis showed that the studied compound is crystallized in tetragonal P4/nmm space group with lattice parameters a = 3.9911(3) {\AA}, c = 13.3830(2) {\AA}. Bulk superconductivity is established in NdO0.5F0.5BiS2 at 5K by both transport and magnetic measurements. Electrical transport measurements showed superconducting Tc onset at 5.2K and Tc ({\rho}=0) at 4.7K. Under applied magnetic field both Tc onset and Tc ({\rho} =0) decrease to lower temperatures and an upper critical field [Hc2(0)] of above 23kOe is estimated. Both AC and DC magnetic susceptibility measurements showed bulk superconductivity below 5K. Isothermal magnetization (MH) exhibited typical type II behavior with lower critical field (Hc1) of around 15Oe. Isothermal magnetization (MH) exhibited typical type-II behavior with lower critical field (Hc1) of around 15Oe. Specific heat [Cp(T)] is investigated in the temperature range of 1.9-50K in zero external magnetic field. A Schottky-type anomaly is observed at low temperature below 7K. This low temperature Schottky can be attributed to the change in the entropy of the system.Comment: 10 pages text + Figs (New Version):comments/suggestion welcome ([email protected]

Bulk Superconductivity in Bismuth-oxy-sulfide Bi4O4S3

Very recent report [1] on observation of superconductivity in Bi4O4S3 could potentially reignite the search for superconductivity in a broad range of layered sulphides. We report here synthesis of Bi4O4S3 at 5000C by vacuum encapsulation technique and basic characterizations. Detailed structural, magnetization, and electrical transport results are reported. Bi4O4S3 is contaminated by small amounts of Bi2S3 and Bi impurities. The majority phase is tetragonal I4/mmm space group with lattice parameters a = 3.9697(2){\AA}, c = 41.3520(1){\AA}. Both AC and DC magnetization measurements confirmed that Bi4O4S3 is a bulk superconductor with superconducting transition temperature (Tc) of 4.4K. Isothermal magnetization (MH) measurements indicated closed loops with clear signatures of flux pinning and irreversible behavior. The lower critical field (Hc1) at 2K, of the new superconductor is found to be ~39 Oe. The magneto-transport R(T, H) measurements showed a resistive broadening and decrease in Tc (R=0) to lower temperatures with increasing magnetic field. The extrapolated upper critical field Hc2(0) is ~ 310kOe with a corresponding Ginzburg-Landau coherence length of ~100{\AA} . In the normal state the {\rho} ~ T2 is not indicated. Our magnetization and electrical transport measurements substantiate the appearance of bulk superconductivity in as synthesized Bi4O4S3. On the other hand same temperature heat treated Bi is not superconducting, thus excluding possibility of impurity driven superconductivity in the newly discovered Bi4O4S3 superconductor.Comment: 12 pages Text + Fig

Magnetization and Magneto-resistance in Y(Ba1-xSrx)2Cu3O7-{\delta} (x = 0.00 - 0.50) superconductor

Here we present the magnetic properties and upper critical field (BC2) of polycrystalline Y(Ba1-xSrx)2Cu3O7-{\delta} superconductors, which are being determined through detailed ac/dc susceptibility and resistivity under magnetic field (RTH) study. All the samples are synthesized through solid state reaction route. Reduction in Meissner fraction (the ratio of field cooled to zero field cooled magnetization) is observed with increasing Sr content, suggesting occurrence of flux pining in the doped samples. The ac susceptibility and resistivity measurements reveal improved grain couplings in Sr substituted samples. Consequently the inter-grain critical current density (Jc), upturn curvature near the Tc in temperature dependence of upper critical field [BC2(T)], and BC2 are enhanced. Both Jc and BC2 increase in lower Sr substitution (up to x = 0.10) samples followed by decrease in higher doping due to degradation in effective pining and grain coupling.Comment: 17 pages text + Figs, [email protected]

Functional Data Analysis of Amplitude and Phase Variation

The abundance of functional observations in scientific endeavors has led to a significant development in tools for functional data analysis (FDA). This kind of data comes with several challenges: infinite-dimensionality of function spaces, observation noise, and so on. However, there is another interesting phenomena that creates problems in FDA. The functional data often comes with lateral displacements/deformations in curves, a phenomenon which is different from the height or amplitude variability and is termed phase variation. The presence of phase variability artificially often inflates data variance, blurs underlying data structures, and distorts principal components. While the separation and/or removal of phase from amplitude data is desirable, this is a difficult problem. In particular, a commonly used alignment procedure, based on minimizing the $\mathbb{L}^2$ norm between functions, does not provide satisfactory results. In this paper we motivate the importance of dealing with the phase variability and summarize several current ideas for separating phase and amplitude components. These approaches differ in the following: (1) the definition and mathematical representation of phase variability, (2) the objective functions that are used in functional data alignment, and (3) the algorithmic tools for solving estimation/optimization problems. We use simple examples to illustrate various approaches and to provide useful contrast between them.Comment: Published at http://dx.doi.org/10.1214/15-STS524 in the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org