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Fermi arcs, pseudogap and collective excitations in doped Sr2IrO4: A generalized fluctuation exchange study

Motivated by recent experimental measurements, we study the quasiparticle spectra and the collective excitations in doped Sr$_2$IrO$_4$, in which the interesting interplay between the electronic correlations and strong spin-orbital coupling (SOC) exists. To include the SOC, we use the Hugenholtz diagrams to extend the fluctuation exchange (FLEX) approach to the case where the SU(2) symmetry can be broken. By using this generalized FLEX method, we find a weak pseudogap behavior near $(π,0)$ in the slightly electron-doped system, with the corresponding Fermi arc formed by the partial destruction of Fermi surface. Similar features also appear in the hole-doped system, however, the position of the Fermi arc is rotated $45^\circ$ with respect to the former. These results are consistent with the recent angle-resolved photoemission spectra in Sr$_2$IrO$_4$. We demonstrate that these anomalous features are mainly caused by the isospin fluctuations derived from the effective $J_{\text{eff}}=1/2$ doublet.