Abstract
Scanning tunneling spectroscopy (STS) experiments were performed on the (001) and (111) surfaces of single crystalline magnetite. Room temperature spectra exhibit a gap around . The importance of perfect surface order to the existence of this gap is illustrated. STS is also carried out on the (111) surface, at 140 and , just above and below the Verwey transition temperature , respectively. It is confirmed that above a gap exists in the surface density of states (DOS) around . Furthermore, broad bands are resolved on both sides of , with peaks centered on and . Below it is shown that the value of the gap in the surface DOS remains similar, however, the peaks resolved in the conduction and valence bands shift markedly away from . The similarity of the gap value before and after the transition points away from an ionic charge ordering occurring at the magnetite surface below . However, the shifting of the bands points to a certain degree of electronic ordering or charge disproportionation playing an integral part in the Verwey transition, at the magnetite surface.
- Received 11 May 2006
DOI:https://doi.org/10.1103/PhysRevB.74.085416
©2006 American Physical Society