Anomalous Impurity-Induced Charge Modulations in Black Phosphorus

We use scanning tunneling microscopy to investigate charge modulations induced by ionized indium impurities on the surface of black phosphorus. When individual impurities are switched into a negatively charged state by the STM tip, periodic charge modulations emerge around the impurity center and are strictly confined by the nanoscale impurity potential. The resulting patterns form a distorted triangular lattice whose periodicity remains unchanged over a wide range of positive bias. Notably, the anisotropy of these local charge modulations is opposite to that expected from the anisotropic Fermi surface of black phosphorus, ruling out a simple band-structure-based interpretation. These results demonstrate that impurity engineering enables the creation and manipulation of localized charge-ordered states in low-dimensional semiconductors.