Rajveer Jha

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

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) A and c = 13.3830(2) A. 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.

Appearance of bulk superconductivity under hydrostatic pressure in Sr0.5RE0.5FBiS2 (RE = Ce, Nd, Pr, and Sm) compounds

We report the appearance of superconductivity under hydrostatic pressure (0–2.5 GPa) in Sr0.5RE0.5FBiS2 with RE = Ce, Nd, Pr, and Sm. The studied compounds, being synthesized by solid state reaction route, are crystallized in tetragonal P4/nmm space group. At ambient pressure, though the RE = Ce exhibits the onset of superconductivity below 2.7 K, the Nd, Pr, and Sm samples are not superconducting down to 2 K. With application of hydrostatic pressure (up to 2.5 GPa), superconducting transition temperature (Tc) is increased to around 10 K for all the studied samples. The magneto-resistivity measurements are carried out on all the samples under 2.5 GPa pressure and their upper critical fields (Hc2) are determined. The superconductivity of these compounds appears to be quite robust against magnetic field. Summarily, the Sr0.5RE0.5FBiS2 compounds with RE = Ce, Nd, Pr, and Sm are successfully synthesized and superconductivity is induced in them under hydrostatic pressure.

Impact of Hydrostatic Pressure on Superconductivity of Sr0.5La0.5FBiS2

We report the impact of hydrostatic pressure (0–1.97 GPa) on superconductivity of recently discovered 2 K 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 10 K with just above 1 GPa pressure, which remains nearly unaltered for studied higher pressures of up to 1.97 GPa. The fivefold increase in Tc accompanied with decrease in normal state resistivity of Sr0.5La0.5FBiS2 with just above 1 GPa pressure calls for the attention of solid state physics community.

Superconducting and magneto-transport properties of BiS2 based superconductor PrO1-xFxBiS2 (x = 0 to 0.9)

We report superconducting properties of PrO1-xFxBiS2 compounds, synthesized by the vacuum encapsulation technique. The synthesized PrO1-xFxBiS2 (x = 0.1, 0.3, 0.5, 0.7, and 0.9) samples are crystallized in a tetragonal P4/nmm space group. Both transport and DC magnetic susceptibility measurements showed bulk superconductivity below 4 K. The maximum Tc is obtained for x = 0.7 sample. Under applied magnetic field, both Tconset and Tc (ρ = 0) decrease to lower temperatures. We estimated highest upper critical field [Hc2(0)] for PrO0.3F0.7BiS2 sample to be above 4 T (Tesla). The thermally activated flux flow activation energy (U0) is estimated 54.63 meV in 0.05 T field for PrO0.3F0.7BiS2 sample. Hall measurement results showed that electron charge carriers are the dominating ones in these compounds. Thermoelectric effects (Thermal conductivity and Seebeck coefficient) data suggest strong electron-electron correlations in this material.

Robust superconductivity with large upper critical field in Nb2PdS5

We report synthesis, structural details, and complete superconducting characterization of very recently discovered [Q. Zhang, Sci. Rep. 3, 1446 (2013)] Nb2PdS5 new superconductor. The synthesized compound is crystallized in monoclinic structure with C2/m (#12) space group. Bulk superconductivity is seen in both ac/dc magnetic susceptibility and electrical resistivity measurements with superconducting transition temperature (Tc) at 6 K. The upper critical field (Hc2) being estimated from high field magneto-transport [ρ(T)H] measurements is above 240 kOe. The estimated Hc2(0) is clearly above the Pauli paramagnetic limit of ∼1.84Tc. Heat capacity (Cp) measurements show clear transition with well defined peak at Tc, but with lower jump than as expected for a Bardeen–Cooper–Schrieffer type superconductor. The Sommerfeld constant (γ) and Debye temperature (ΘD) as determined from low temperature fitting of CP(T) data are 32 mJ/mole-K2 and 263 K, respectively. Hall coefficients and resistivity in conjugation wit...

Magnetization and magneto-resistance in Y(Ba1−xSrx)2Cu3O7−δ (x = 0.00–0.50) superconductors

Here we present the magnetic properties and upper critical field (BC2) of polycrystalline Y(Ba1?xSrx)2Cu3O7?? superconductors, which are determined through detailed ac/dc susceptibility and resistivity under magnetic field study. All the samples are synthesized through the solid state reaction route. Reduction in the Meissner fraction (the ratio of field cooled to zero field cooled magnetization) is observed with increasing Sr content, suggesting the occurrence of flux pinning in the doped samples. The ac susceptibility and resistivity measurements reveal improved grain coupling in Sr substituted samples. Consequently the inter-grain critical current density (Jc), upward curvature near Tc in the temperature dependence of the 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 for higher doping due to degradation in the effective pinning and grain coupling.

Specific Heat of Robust Nb2PdS5 Superconductor

We report specific heat under different magnetic fields for recently discovered quasi-one-dimensional Nb2PdS5 superconductor. The studied compound is superconducting below 6 K. Nb2PdS5 is quite robust against magnetic field with dHc/dT of −42 kOe/K. The estimated upper critical field [ Hc2(0)] is 190 kOe, clearly surpassing the Pauli-paramagnetic limit of 1.84 Tc. Low-temperature heat capacity in superconducting state of Nb2PdS5 under different magnetic fields showed s-wave superconductivity with two different gaps. Two quasilinear slopes in Somerfield coefficient (γ) as a function of applied magnetic field and two-band behavior of the electronic heat capacity demonstrate that Nb2PdS5 is a multiband superconductor in weak coupling limit with ΔC/ γTc = 0.9.

Pressure enhanced superconductivity at 10 K in La doped EuBiS2F

We have investigated the effect of La doping and high pressure on superconducting properties of EuBiS2F, which is a newly discovered superconducting material (T-c similar to 0.3 K) (Zhai et al (2014) Phys. Rev. B 90 064518). An enhancement of T-c to 2.2 K is observed in Eu0.5La0.5BiS2F. Upon application of pressure T-c is further enhanced up to similar to 10 K (P = 2.5 GPa). Eu0.5La0.5BiS2F is semiconducting down to 3 K. The onset of a superconductivity-like feature is seen at 2.2 K at ambient pressure. At a pressure above 1.38 GPa, the T-c(onset) remains invariant at 10 K but the T-c(rho = 0) is increased to above 8.2 K. There is a possible crystallographic transformation by application of pressure from a structure of low T-c to a structure corresponding to high T-c.

Superconductivity at 4.4 K in PdTe2 Chains of a Ta-Based Compound

Superconductivity in PdTe2 heavy transition metal-based compounds is a rapidly developing field in condensed matter physics community. Here, we report superconductivity in a nominal ternary telluride Ta2Pd0.97Te6 compound, which is synthesized in sealed evacuated quartz ampoule. The resultant compound is crystallized in layered monoclinic Ta4Pd3Te16 phase with space group C2/m, having lattice parameters a = 21.304(6)Å, b = 3.7365(7)Å and c = 17.7330Å with β = 120.65(1)∘. Both transport and magnetic measurements demonstrated bulk superconductivity at 4.4 K in studied polycrystalline sample. The metallic normal state conductivity can be well ascribed to Fermi liquid behaviour. The superconducting upper critical field of the compound is determined to be 5.5 T based on magnetoresistivity measurements.

PdTe: a 4.5 K type-II BCS superconductor

We report on the structure and physical properties of the polycrystalline PdTe superconductor, which is synthesized by the solid state reaction route via the quartz vacuum encapsulation technique at 750 °C. The as synthesized compound is crystallized in hexagonal crystal structure with P63/mmc space group. Both transport and magnetic measurements showed that PdTe is a bulk superconductor below 4.5 K. Isothermal magnetization (MH) and magneto-transport (R(T)H) measurements provided the values of the lower (Hc1) and upper (Hc2) critical fields as 250 Oe and 1200 Oe respectively at 2 K, establishing that the compound is clearly a type-II superconductor. The coherence length (ξ0) and Ginzburg–Landau parameter (κ) are estimated from the experimentally determined upper and lower critical fields, and are 449 A and 1.48 respectively. Thermodynamic heat capacity measurements under different magnetic fields, i.e. Cp(T)H, showed a clear transition at 4.5 K (Tc), which shifts gradually to lower temperatures with application of field. The values of Debye temperature (ΘD) and electronic specific heat coefficient (γ) obtained from Cp(T) data are found to be 203 K and 6.01 mJ mol−1 K−2. The observed specific heat jump (ΔC/γTc) is 1.33, thus suggesting a possible weak coupling case for the PdTe superconductor.