Pressure-induced coexistence of filamentary superconductivity, orthorhombic stripe-type antiferromagnetic state and re-entrant tetragonal phase in the iron-based superconductor Ba_1-xK_xFe₂As₂

While for Co-doped BaFe₂As₂ materials, pressure and an increase in Co concentration has a similar doping effect, and it is observed that the superconducting transition temperature rises to a maximum T_c and then decreases as soon as the overdoped regime is reached, K-doped BaFe₂As₂ shows a distinct behavior. If a certain pressure is reached in materials with a K concentration between 16 and 19%, it was observed that under a moderate pressure in the GPa range T_c saturates and an intermediate phase appears between the antiferromagnetic transition and T_c [E. Hassinger et al., Phys. Rev. B 86, 140502(R) (2012)]. We report a large variety of experimental quantities measured under the influence of quasi-hydrostatic pressure up to several GPa, including resisitivity, Hall effect, specific heat, and the thermoelectrical Nernst and Seebeck coefficients. We find that under quasi-hydrostatic conditions, the transition into the intermediate phase is partially suppressed and a complex coexistence of filamentary superconductivity, orthorhombic stipe-type antiferromagnetic order and a re-entrant tetragonal phase in form of an inhomogeneous phase separation is found instead.