Disorder induced correlation gap suppresses superconductivity in the 5$d$ metallic perovskite Ba$_{1-x}$La$_{x}$PbO$_{3}$

We report the synthesis and characterization of the electronic structure of thin films of the perovskite Ba$_{1-x}$La$_{x}$PbO$_{3}$ grown by oxide molecular-beam epitaxy. Using angle-resolved photoemission spectroscopy our measurements reveal a Fermi surface consistent with density functional calculations at low doping, but indicate the formation of an energy gap at higher doping values ($x$ $\sim$ 0.2), consistent with electrical transport measurements. By comparison with temperature-dependent point contact tunneling spectroscopy measurements, we show this behavior is consistent with a disorder-driven correlation gap. Moreover the photoemission data reveal a density of states that is not linear at high binding energies, suggesting discrepancy with previous tunneling density of states measurements of superconducting oxides.