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We have synthesized and studied the transport properties of FeTexSe1-x (x = 0.4, 0.46, 0.5, 0.54, and 0.58) single crystals grown by slow cooling method and found a sharp increase of Tc up to x = 0.46 followed by a moderate decrease of Tc up to x = 0.58. We present the temperature dependence of electrical resistivity under various pressures up to ~ 2.5 GPa, and the pressure dependence of Tc shows positive pressure coefficients of ~ 2.7 K/GPa and ~ 3.33 K/GPa for x = 0.46 and x = 0.54, respectively, up to 2 GPa followed by a decreasing trend with marginal variation of Tc with negative pressure coefficients of − 0.602 K GPa−1 (x = 0.46) and − 0.7 K GPa−1 (x = 0.54) at maximum pressure of 2.5 GPa. Furthermore, both normal state resistivity and activation energy decrease sharply, and it suggests that the reduction of net electron-phonon scattering and densities of states (DOS) at the Fermi surface with application of pressure leads to enhancement of metallic behavior in FeSe systems.

We report the effect of high pressure on the superconducting, vortex pinning, and structural properties of a polycrystalline non-centrosymmetric superconductor Re6Hf. The superconducting transition temperature, Tc, reveals a modest decrease as pressure P increases with a slope -0.046 K/GPa (-0.065 K/GPa) estimated from resistivity measurements up to 8 GPa (magnetization measurement ~ 1.1 GPa). Structural analysis up to ~18 GPa reveals monotonic decreases of lattice constant without undergoing any structural transition and a high value of bulk modulus B0= 333.63 GPa, indicating the stability of the structure. Furthermore, the upper critical field and lower critical field at absolute temperature (Hc2(0) & Hc1(0)) decreases slightly from the ambient pressure value as pressure increases up to 2.5 GPa. In addition, up to P ~ 2.5 GPa using thermally activated flux flow of vortices revealed a double linearity field dependence of activation energy of vortices, confirming the coexistence of single and collective pinning vortex states. Moreover, analysis of critical current density using the collective pinning theory showed the transformation of {\delta}Tc to {\delta}l pinning as pressure increases, possibly due to migration of grain boundaries. Besides, the band structure calculations using density functional theory show that density of states decreases modestly with pressure, which may be a possible reason for such a small decrease in Tc by pressure., Comment: 14 pages, 10 figures, Article

We have studied the effect of hydrostatic pressure on the superconducting and normal state properties of the non-centrosymmetric superconductor Re5.5Ta using magnetotransport, magnetization, and band structure studies. The superconducting transition temperature ( T c ) reveals a modest decrease of ∼0.52 K as the external pressure is raised to 8 GPa. We found the Maki parameter, 1,$?> α M > 1 , both at ambient and high pressures, suggesting the significant role of the Pauli pair breaking effect. Furthermore, the lower critical field was found to decrease with a rate of −1.74 mT GPa−1 as pressure increases to 1.05 GPa. Analysis of the thermally activated flux flow region of ρ T , H using the Arrhenius equation reveals the coexistence of single and collective vortex states. Further analysis of the critical current density indicates that the surface and volume pinning centers coexist and remain unaffected with varying pressure. Band structure calculations were performed using density functional theory and reveal a large bulk modulus, B 0 ∼ 289 GPa with B 0 ′ ∼ 3.7, suggesting poor compressibility. In addition, we found that the density of states at the Fermi level barely reduces, even at pressures of up to 20 GPa. This is consistent with the experimental observation of robust superconductivity under compression.