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

We report the effect of high pressure on the superconducting, vortex pinning, and structural properties of a polycrystalline, noncentrosymmetric superconductor Re₆Hf . The superconducting transition temperature,T_c , reveals a modest decrease as pressure (P ) increases with a slope of −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 [H_{c 2}(0 ) and H_{c 1}(0 ) ] decrease slightly from the ambient pressure value as pressure increases up to 2.5 GPa. In addition, analysis of ρ (T ,H ) up to P ∼ 2.5 GPa using thermally activated flux flow of vortices revealed a double linearity field dependence of activation energy of vortices [U_o(H ) ] , 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 δ T_c to δ 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 T_c by pressure.