Temperature- and pressure-dependent electronic structure evolution of quasi-one-dimensional iron chalcogenide ladder compounds, BaFe₂S₃, and BaFe₂Se₃: optical studies and DFT calculations

Since the discovery of a pressure-induced iron-based superconductor, BaFe₂S₃ (BFS), intensive studies have been performed on BFS and a similar compound BaFe₂Se₃ (BFSe). Both compounds are antiferromagnetic insulators, with increasing pressure they show metallic phases and eventually become superconductors under very high pressure. We measured reflectance spectra of those two compounds by controlling two experimental tuning parameters: temperature and pressure. From our temperature-dependent measured reflectance spectra of both samples using polarized lights, we obtained anisotropic optical conductivity along two crystal axes. We observed bandgaps in both samples along the ladder direction at low temperature. We also observed pressure-induced insulator-metal transitions (IMT) in both samples from our pressure-dependent measured mid-infrared reflectance spectra of both samples at 300 K using diamond anvil cells. The density functional theory calculations were also performed to understand the measured experimental spectra. In this presentation, we will present our results and discuss on them.