  In transition metal perovskites (ABO3) most physical properties are tunable
by structural parameters such as the rotation of the BO6 octahedra. Examples
include the N\'eel temperature of orthoferrites, the conductivity of
mixed-valence manganites, or the band gap of rare-earth scandates. Since oxides
often host large internal electric dipoles and can accommodate heavy elements,
they also emerge as prime candidates to display Rashba spin-orbit coupling,
through which charge and spin currents may be efficiently interconverted.
However, despite a few experimental reports in SrTiO3-based interface systems,
the Rashba interaction has been little studied in these materials, and its
interplay with structural distortions remain unknown. In this Letter, we
identify a bismuth-based perovskite with a giant, electrically-switchable
Rashba interaction whose amplitude can be controlled by both the ferroelectric
polarization and the breathing mode of oxygen octahedra. This particular
structural parameter arises from the strongly covalent nature of the Bi-O
bonds, reminiscent of the situation in perovskite nickelates. Our results not
only provide novel strategies to craft agile spin-charge converters but also
highlight the relevance of covalence as a powerful handle to design emerging
properties in complex oxides.
