Coherent quasiparticles with a small fermi surface in lightly doped Sr₃Ir₂O₇

We characterize the electron doping evolution of (Sr_1-xLa_x)₃Ir₂O₇ by means of angle-resolved photoemission. Concomitant with the metal insulator transition around x ≈ 0.05 we find the emergence of coherent quasiparticle states forming a closed small Fermi surface of volume 3x/2, where x is the independently measured La concentration. The quasiparticle weight Z remains large along the entire Fermi surface, consistent with the moderate renormalization of the low-energy dispersion, and no pseudogap is observed. This indicates a conventional, weakly correlated Fermi liquid state with a momentum independent residue Z ≈ 0.5 in lightly doped Sr₃Ir₂O₇.