Track the bands: Verwey phase transition in single magnetite nanocrystals

Verwey transition in magnetite is known for ages as an opening of bandgap below a transition temperature. With scanning tunneling spectroscopy (STS) in obtaining density of states in an extremely localized manner, STS has revealed Verwey transition in a single nanocrystal of Fe₃O₄ as a transition between a gapless state and a gapped state at around 110 K. In this work, we deliberate on the band-edges responsible during opening/collapse of the bandgap. We observe that the change in the conduction band is larger than the change in the valence band during the transition. The larger change in conduction band position has been explained in terms of antibonding nature of iron and oxygen orbitals in forming the conduction band and thereby its proneness to be affected upon the phase-change involved during a Verwey transition. The non-bonding nature of oxygen in forming the valence band has made the band less vulnerable during the transition. (paper)