  Single molecular electrets exhibiting single molecule electric polarization
switching have been long desired as a platform for extremely small non-volatile
storage devices, although it is controversial because of the poor stability of
single molecular electric dipoles. Here we study the single molecular device of
GdC82, where the encapsulated Gd atom forms a charge center, and we have
observed a gate controlled switching behavior between two sets of single
electron transport stability diagrams. The switching is operated in a
hysteresis loop with a coercive gate field of around 0.5Vnm. Theoretical
calculations have assigned the two conductance diagrams to corresponding energy
levels of two states that the Gd atom is trapped at two different sites of the
C82 cage, which possess two different permanent electrical dipole orientations.
The two dipole states are stabilized by the anisotropic energy and separated by
a transition energy barrier of 70 meV. Such switching is then accessed to the
electric field driven reorientation of individual dipole while overcoming the
barriers by the coercive gate field, and demonstrates the creation of a single
molecular electret.
