  In Sr2IrO4 and Sr3Ir2O7, correlations, magnetism and spin-orbit coupling
compete on similar energy scales, creating a new context to study
metal-insulator transitions (MIT). We use here Angle-Resolved photoemission to
investigate the MIT as a function of hole and electron doping in Sr3Ir2O7,
obtained respectively by Ir/Rh and Sr/La substitutions. We show that there is a
clear reduction as a function of doping of the gap between a lower and upper
band on both sides of the Fermi level, from 0.2eV to 0.05eV. Although these two
bands have a counterpart in band structure calculations, they are characterized
by a very different degree of coherence. The upper band exhibits clear
quasiparticle peaks, while the lower band is very broad and loses weight as a
function of doping. Moreover, their ARPES spectral weights obey different
periodicities, reinforcing the idea of their different nature. We argue that a
very similar situation occurs in Sr2IrO4 and conclude that the physics of the
two families is essentially the same.
