Correlated vs. conventional insulating behavior in the Jeff=1/2 vs. 3/2 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) = 1/2 and 3/2 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) = 1/2 state exhibits a strong temperature dependence and its gap softens with increasing temperature approaching T-N, while the nearly fully occupied J(eff) = 3/2 state which remains nearby in energy exhibits negligible changes with temperature.