Disorder Driven Mott Gap Collapse accompanied by the Emergence of a Pseudogap

The origin of the pseudogap in doped Mott insulators remains one of the biggest mysteries in correlated electron systems. Of the potential causes for a pseudogap, disorder, while ubiquitous, is least invoked and most poorly understood. To investigate the role of disorder in destabilizing a Mott state and realizing a pseudogap state, we use scanning tunneling microscopy and spectroscopy to study isovalent Ru substitutions in Sr₃(Ir_1-xRu_x)₂O₇ (0≤x≤0.5). Ru creates disorder without the complication of additional order parameters and drives the insulator into an antiferromagnetic, metallic state with a pseudogap similar to that seen in other iridates and cuprates. Nanoscale data show that disorder mediates the transition by locally collapsing the Mott gap and this effect can be captured by a minimal Mott-Hubbard model. Our work establishes a novel mechanism for an insulator to metal transition and establishes a central role for disorder in realizing an emergent pseudogap state in doped Mott systems.