  Electrical manipulation of lattice, charge, and spin has been realized
respectively by the piezoelectric effect, field-effect transistor, and electric
field control of ferromagnetism, bringing about dramatic promotions both in
fundamental research and industrial production. However, it is generally
accepted that the orbital of materials are impossible to be altered once they
have been made. Here we use electric-field to dynamically tune the electronic
phase transition in (La,Sr)MnO3 films with different Mn^4+/(Mn^3+ + Mn^4+)
ratios. The orbital occupancy and corresponding magnetic anisotropy of these
thin films are manipulated by gate voltage in a reversible and quantitative
manner. Positive gate voltage increases the proportion of occupancy of the
orbital and magnetic anisotropy that were initially favored by strain
(irrespective of tensile and compressive), while negative gate voltage reduces
the concomitant preferential orbital occupancy and magnetic anisotropy. Besides
its fundamental significance in orbital physics, our findings might advance the
process towards practical oxide-electronics based on orbital.
