Evolution of in-gap spectral weight in electron- and hole-doped Sr₂IrO₄ studied by time-resolved optical reflectivity

The 5d transition metal oxide Sr₂IrO₄ realizes an unusual J_eff = 1/2 antiferromagnetic Mott insulating ground state that is stabilized by an interplay of strong spin-orbit coupling and on-site Coulomb repulsion. Motivated by its structural and magnetic similarities to La₂CuO₄ - the parent compound of cuprate high-Tc superconductors - there have recently been intensive efforts to study the electron-doped (Sr_1-xLa_x)₂IrO₄ series and the hole-doped Sr₂Ir_1-xRh_xO₄ series. In both cases, light substitution levels trigger a collapse of long-range antiferromagnetic order and an emergence of unusual metallic states with residual pseudogaps. Here we study the doping evolution of the electronic density of states in both (Sr_1-xLa_x)₂IrO₄ and Sr₂Ir_1-xRh_xO₄ using ultrafast time-resolved optical reflectivity. Our results reveal a similar development of in-gap states and a shifting of the chemical potential upon crossing over from Mott insulator to metal on both electron- and hole-doped sides of the phase diagram.