Figure 5.

ρ_xx vs. V_g with varying delay time (a). Dual Dirac peaks switch position with increasing delay. ρ_xx vs. time (b) and n vs. time (c) showing ultra-slow relaxation of surface dipoles. All measurements begin at stable state of +200 V. Carrier type switches when ramped below +50 V with no change at values above. At +50 V the carrier type switches twice. Surface dipole model (d) showing oxygen atoms (open circles) puckered out from the surface at zero applied field. At +200 V, the applied E- field causes oxygen to move toward the Sr or Ti atoms (black circles). This decreases the dipole moment.