We investigated the electronic superstructure of graphite surface in the vicinity to monoatomic armchair step edges with scanning tunneling microscopy and spectroscopy. Only the ($\sqrt{ 3}\times\sqrt{ 3}$)$\textit{ R}$30$^{ \circ}$ superstructure is visualized near atomically clean armchair edges, while the honeycomb superstructure is absent. The spectroscopic mapping near the clean armchair edge clearly reveals the ($\sqrt{ 3}\times\sqrt{ 3}$)$\textit{ R}$30$^{ \circ}$ superstructure on both sides of the step edge. We have also visualized a mixture of ($\sqrt{ 3}\times\sqrt{ 3}$)$\textit{ R}$30$^{ \circ}$ and honeycomb superstructures near structurally defective armchair edges. Our results suggest that the honeycomb superstructure pattern results from superposition of two sets of ($\sqrt{ 3}\times\sqrt{ 3}$)$\textit{ R}$30$^{ \circ}$ superstructure with different phases. Our observation solves the mystery of the coexistence of two types of superstructures reported by prior studies.
Categories: cond-mat.str-el cond-mat.mes-hall