Tunable Valley and Spin Polarizations in BiXO 3 /BiIrO 3 (X = Fe, Mn) Ferroelectric Superlattices.

The generation and modulation on valley and spin degrees of freedom are essential for multifunctional electronic devices. Herewith, the electronic structures in BiXO3 /BiIrO3 (X = Fe, Mn) ferroelectric superlattices are studied by first-principles calculations with spin-orbital coupling. Different from the previous BiAlO3 /BiIrO3 system, both valley and spin polarizations in bilayered BiIrO3 are achieved in BiXO3 /BiIrO3 superlattices, where the spin polarization in the valley can be engineered by the spin orientation of Fe or Mn owing to the xy-plane orbitals. Especially, the relatively parallel and antiparallel directions of ferroelectric polarization in BiFeO3 and BiIrO3 can switch the valley injection in BiFeO3 /BiIrO3 superlattices. Overall, the tunable valley and spin polarizations in BiFeO3 /BiIrO3 ferroelectric superlattices pave a way for developing nonvolatile data memories and valley-spin devices.