The ways in which pressure affects both the fundamental physics, and macroscopic material properties of iron-based superconductors provides an avenue with great potential for both the exploration of the theoretical underpinnings of superconductivity, and its immediate impact on the critical current density (Jc), and superconducting transition temperature (Tc) – parameters which are of utmost importance to the development of engineering applications.
Our research is centred around systematically evaluating the effect of incremental changes in applied hydrostatic pressure on single crystals of phosphorous (P) and nickel (Ni) doped BaFe-2As2 (Ba122). We aim to begin elucidating the difference between the effect of external pressures, and isovalent/electron doping, providing necessary context for the exploration of material properties which affect the current carrying capabilities of bulk superconductors.
Magnetic measurements reveal that the anisotropic compressibility of Ba122 materials results in a non-linear response of Tc, and Jc, to hydrostatic pressure. For P-doped samples, pressures below 0.6 GPa suppress Tc by as much as 50 %, losses which are recovered upon further pressurisation up to 1.2 GPa. This phenomenon is present regardless of the level of doping, and leads to a sensitive dependence of Jc on applied pressures in this range. Furthermore, the same procedure presented for Ni-doped samples shows that this effect is significantly diminished upon reaching an optimal doping fraction, providing an interesting contrast to further understand the role of charge doping in Ba122.
These results fill out the superconductor communities body of knowledge, and provide a glimpse into the still opaque nature of superconductivity in these materials.
Keywords: Iron pnictide, Quantum critical point, Hydrostatic pressure, Critical current density