Superconductivity in layered CeO0.5F0.5BiS2

We report appearance of superconductivity in CeO0.5F0.5BiS2. The bulk polycrystalline samples CeOBiS2 and CeO0.5F0.5BiS2 are synthesized by conventional solid state reaction route via vacuum encapsulation technique. Detailed structural analysis showed that the studied CeO0.5F0.5BiS2 compound is crystallized in tetragonal P4/nmm space group with lattice parameters a = 4.016(3) A, c = 13.604(2) A. DC magnetization measurement (MT-curve) shows the ferromagnetic signal at the low temperature region. The superconductivity is established in CeO0.5F0.5BiS2 at Tconset = 2.5K by electrical transport measurement. Under applied magnetic field both Tc onset and Tc ({\rho} =0) decrease to lower temperatures and an upper critical field [Hc2(0)] above 1.2Tesla is estimated. The results suggest coexistence of ferromagnetism and superconductivity for the CeO0.5F0.5BiS2 sample.Comment: 9 pages text + Fig

Effect of Se doping in recently discovered layered Bi4O4S3 Superconductor

We report suppression of superconductivity in Bi4O4S3 compound by Se doping at S site. Bulk polycrystalline samples are synthesized by solid state reaction route. The Rietveld refined of XRD data of all the studied samples show that the same are crystallized in tetragonal I4/mmm space group with slightly increased c lattice constant with the Se doping. Superconductivity is observed at below 4.5 K in both dc magnetization and resistivity with temperature measurements for all Bi4O4S3-xSex (x = 0, 0.03, 0.09 and 0.15) samples, though the same is decreased slightly with increase in Se content. The upper critical field of the Bi4O4S3 is estimated from resistivity under magnetic field [R(T)H] measurements of up to 2T (Tesla), and the same decreases for Se doped samples. The flux flow activation energies being obtained by fitting to the the Arrhenius equation are 18.60 meV for Bi4O4S3, 13.69 meV for Bi4O4S2.97Se0.03 and 13.16 meV for Bi4O4S2.85Se0.15 samples in applied magnetic field of 200 Oe. In conclusion the S site Se substitution showed detrimental effect on superconductivity of Bi4O4S3.Comment: 9 pages text + Fig

Impact of hydrostatic pressure on superconductivity of Sr0.5La0.5FBiS2

We report the impact of hydrostatic pressure (0-1.97GPa) on superconductivity of recently discovered 2K superconductor Sr0.5La0.5FBiS2. Resistivity under pressure measurements are performed by using HPC-33 Piston type pressure cell with Quantum design DC resistivity Option. The superconducting transition temperature (Tc) is increased by 5 fold to around 10K with just above 1GPa pressure, which remains nearly unaltered for studied higher pressures of up to 1.97GPa. The fivefold increase in Tc of Sr0.5La0.5FBiS2 with just above 1GPa pressure suggests very strong electron correlations in these systems and the same calls for the attention of solid state physics community.Comment: 11 pages text + Figs: Five fold increase in Tc with Just above 1GP

Magnetotransport studies of FeSe under hydrostatic pressure

The discoveries of iron-based superconductors with relatively high transition temperature are under intense experimental and theoretical investigation. Here we present magnetotransport measurements on FeSe superconductor under hydrostatic pressure. We show that in Fe-deficient tetragonal FeSe binary compound, the onset of superconducting transition is almost doubled under 1.98GPa pressure and the estimated upper critical field of 26.7Tesla is increased to 47.5Tesla.Comment: Short MS: 8 pages Text + Figs. Pressure induced increase in Tc and pinnin

AC susceptibility study of superconducting YBa2Cu3O7:Agx bulk composites (x = 0.0-0.20): The role of intra and inter granular coupling

We report the effect of silver addition on superconducting performance of bulk YBCO (YBa2Cu3O7) superconductor. All the studied samples are prepared by conventional solid-state reaction method. Rietveld fitted X-ray diffraction data confirmed the single phase formation for all the studied samples. Detailed AC susceptibility measurements as a function of driven AC amplitude (1Oe-17Oe) of these samples revealed the enhancement of grains coupling with increasing Ag content in YBCO+Agx composite system. 10wt% Ag added YBCO superconductors exhibited the optimum inter granular coupling. The Scanning Electron Microscopy (SEM) observations indicate an increase in the grains connectivity in terms of narrow grain boundaries for doped samples. The average grain size is found to increase with Ag doping. It is concluded that limited addition of Ag in bulk YBCO superconductor significantly improves the grains coupling and as result optimum superconducting performance. YBCO+Ag composites could prove to be potential candidates for bulk superconducting applications of the studied high Tc system.Comment: 15 pages of text + Fig

Impact of Gd doping on morphology and superconductivity of NbN sputtered thin films

We report effect of Gd inclusion in the NbN superconductor thin films. The films are deposited on single crystalline Silicon (100) by DC reactive sputtering technique i.e., deposition of Nb and Gd in presence of reactive N2 gas. The fabricated relatively thick films (400 nm) are crystallized in cubic structure. These films are characterized for their morphology, elemental analysis and roughness by Scanning Electron Microscopy (SEM), Energy Dispersive X-ray spectroscopy (EDAX) and Atomic Force Microscopy (AFM) respectively. The optimized film (maximum Tc) is achieved with gas ratio of Ar:N2 (80:20) for both pristine and Gd doped films. The optimized NbN film possesses Tc (R=0) in zero and 140kOe fields are at 14.8K and 8.8K respectively. The Gd doped NbN film showed Tc (R=0) in zero and 130kOe fields at 11.2K and 6.8 K respectively. The upper critical field Hc2(0) of the studied superconducting films is calculated from the magneto-transport [R(T)H] measurements using GL equations. It is found that Gd doping deteriorated the superconducting performance of NbN.Comment: 14 pages Text+Figs: comments/suggestions ([email protected])/www.freewebs.com/vpsawana