Superconducting and structural properties of the noncentrosymmetric Re6Hf superconductor under high pressure

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