Evolution of Midgap States and Residual Three Dimensionality in La_2-xSr_xCuO₄

We carry out extensive first-principles doping-dependent computations of angle-resolved photoemission (ARPES) intensities in La_2-xSr_xCuO₄ over a wide range of binding energies. Intercell hopping and the associated three dimensionality, which is usually neglected in discussing cuprate physics, is shown to play a key role in shaping the ARPES spectra. Despite the obvious importance of strong coupling effects (e.g., the presence of a lower Hubbard band coexisting with midgap states in the doped insulator), a number of salient features of the experimental ARPES spectra are captured to a surprising extent when k_z dispersion is properly included in the analysis.