Correlated vs. conventional insulating behavior in the J_eff = ½ vs. ¾ bands in the layered iridate Ba₂IrO₄

We employ molecular beam epitaxy to stabilize Ba₂IrO₄ thin films and utilize in situ angle-resolved photoemission spectroscopy to investigate the evolution of its electronic structure through the Neel temperature T-N. Our measurements indicate that dispersions of the relativistic  J_eff = ½ vs. ¾ bands exhibit an unusual dichotomy in their behavior through the Neel transition. Although the charge gap survives into the paramagnetic state, only the J_eff = ½ state exhibits a strong temperature dependence and its gap softens with increasing temperature approaching T-N, while the nearly fully occupied J_eff = ¾ state which remains nearby in energy exhibits negligible changes with temperature.