Pressure-induced superconductivity in BaFe₂As₂. Optical study

In previous studies, the superconductivity that arises from the antiferromagnetic state with various carrier dopings in iron-pnictide superconductors was demonstrated. Moreover, the external pressure induced superconductivity was shown by transport measurements. External pressure is a clean way to induce superconductivity compared to impurity doping cases. Moreover, it does not introduce additional carriers to the system. In this study, we performed temperature-dependent reflectivity measurements in BaFe₂As₂ parent compound under pressure (up to 5 GPa). At temperatures above the magnetic phase transition, the metallicity of the system is increasing with pressure. At lower temperatures, with increasing pressure the partial suppression of the magnetically ordered (SDW) state and the appearance of the superconducting (SC) state is observed at 3.6 and 4.2 GPa. At these pressures the SDW state and the SC state coexist. Moreover, the SC gap shows a full gap tendency below ∝95 cm^-1.