Poor electronic screening in lightly doped Mott insulators observed with scanning tunneling microscopy

The interpretation of scanning tunneling microscopy (STM) data on poorly metallic materials is challenging: one needs to take into account the partial penetration of the electric field into the sample, the so-called tip-induced band bending (TIBB). This effect is well known from STM experiments on semiconductors, but rarely discussed for correlated-electron systems. The authors find that in the lightly doped Mott insulator (Sr${}_1-x$La${}_x$)${}₂$IrO${}₄$, TIBB is at the root of apparent discrepancies in the gap values measured by photoemission, optical measurements, and STM. They develop a model to extract the intrinsic Mott gap of the system, leading to agreement with results from other techniques.