  Large Rashba effect efficiently tuned by an external electric field is highly
desired for spintronic devices. Using first-principles calculations, we
demonstrate that large Rashba splitting is locked at conduction band minimum in
ferroelectric Bi(Sc/Y/La/Al/Ga/In)O3/PbTiO3 heterostructures where the position
of Fermi level is precisely controlled via its stoichiometry. Fully reversible
Rashba spin texture and drastic change of Rashba splitting strength with
ferroelectric polarization switching are realized in the symmetric and
asymmetric heterostructures, respectively. By artificially tuning the local
ferroelectric displacement and the orbital hybridization, the synergetic effect
of local potential gradient and orbital overlap on the dramatic change of
splitting strength is confirmed. These results improve the feasibility of
utilizing Rashba spin-orbit coupling in spintronic devices.
