Core-state manipulation of single Fe impurities in GaAs with a scanning tunneling microscope

Abstract

We demonstrate that a scanning tunneling microscope tip can be used to manipulate the tightly bound core ($d$-electron) state of single Fe ions embedded in GaAs. Increasing tip-sample voltage removes one $d$ electron from the core of a single Fe, changing the dopant from the (Fe${}^{2+}$)${}^{\ensuremath{-}}$ ionized acceptor state to the (Fe${}^{3+}$)${}^{0}$ isoelectronic state, which alters the spin moment and dramatically modifies the measured local electronic contrast in topographic maps of the surface. Evidence of internal transitions among the $d$ states of the Fe core is also seen in topographic maps where dark anisotropic features emerge from the interference between two paths: the direct tip-sample tunneling and tunneling which excites a $d$-state core exciton of the Fe dopant.