Bistable lattice position of a single magnetic dopant in a semiconductor

Electronic control of the lattice position of individual dopants has been demonstrated recently, including displacement of a single Si dopant in the surface layer of GaAs by a scanning tunneling microscope (STM)[1]. Fe dopants in GaAs have internal spin degrees of freedom associated with their core d states which can also be manipulated using a STM[2]. A reversible and hysteretic change in the topography measured near a single Fe dopant is observed when a negative bias voltage is applied. To determine if a lattice displacement is responsible, we have performed first-principles calculations to evaluate the formation energy of a single Fe atom embedded in GaAs as a function of displacement from the substitutional site. Our calculations support the existence of a second stable configuration, characterized by a displacement accompanied by a change in atomic configuration symmetry about the Fe from four-fold to six-fold symmetry. These results expand the range of demonstrated local configurational changes induced electronically for dopants, and thus may be of use for sensitive control of spin-spin interactions between dopants.\\[4pt] [1] J. K. Garleff et al., Physical Review B 84, 075459 (2011).\\[4pt] [2] J. Bocquel et al., Physical Review B 87, 075421 (2013).