Effect of pressure on the structural phase transition and superconductivity in (Ba_(1-x)K_x)Fe₂As₂ (x = 0 and 0.45) single crystals

The effects of pressure up to $\sim 20$ kbar, on the structural phase transition of lightly Sn-doped BaFe$_2$As$_2$, as well as on the superconducting transition temperature and upper critical field of (Ba$_{0.55}$K$_{0.45}$)Fe$_2$As$_2$ single crystals have been studied. Both transitions decrease with pressure in an almost linear fashion. Under pressure, the upper critical field curve, $H_{c2}(T)$, shifts down in temperature to follow the zero field $T_c$ with very little change in slope.