Abstract
Ferroelectric Rashba semiconductors (FERSC), in which Rashba spin-splitting can be controlled and reversed by an electric field, have recently emerged as a new class of functional materials useful for spintronic applications. The development of concrete devices based on such materials is, however, still hampered by the lack of robust FERSC compounds. Here, we show that the coexistence of large spontaneous polarization and sizeable spin–orbit coupling is not sufficient to have strong Rashba effects and clarify why simple ferroelectric oxide perovskites with transition metal at the B-site are typically not suitable FERSC candidates. By rationalizing how this limitation can be by-passed through band engineering of the electronic structure in layered perovskites, we identify the Bi{}_{2}WO{}_{6} Aurivillius crystal as a robust ferroelectric with large and reversible Rashba spin-splitting, that can even be substantially doped without losing its ferroelectric properties. Importantly, we highlight that a unidirectional spin–orbit field arises in layered Bi{}_{2}WO{}_{6}, resulting in a protection against spin-decoherence.
Highlights
In non-magnetic solids, one can naively expect the energy bands of electrons of up and down spins to be degenerate in absence of magnetic fields
By rationalizing how this limitation can be by-passed through band engineering of the electronic structure in layered perovskites, we identify the Bi2WO6 Aurivillius crystal as a robust ferroelectric with large and reversible Rashba spin-splitting, that can even be substantially doped without losing its ferroelectric properties
They should include heavy ions with large spin–orbit coupling (SOC) exhibiting a significant Rashba spin-splitting (RSS) close to the valence or conduction band edge, which should be reversible with the polarization and, for applications based on spin/charge currents, should survive to appropriate doping
Summary
In non-magnetic solids, one can naively expect the energy bands of electrons of up and down spins to be degenerate in absence of magnetic fields. The Rashba spin precession of a current injected in such materials can be controlled in a non-volatile way by their reversible ferroelectric polarization. In twodimensional ferroelectric materials with in-plane polarization and strong anisotropy in the electronic structure, the spin–orbit field (SOF) was proposed to have unidirectional out-of-plane alignment: ~ΩSOFð~kÞ 1⁄4 αð~P~kÞ 1⁄4 αky^z, where α is a systemdependent coefficient.[9] In such a case, injected electrons with in-plane spins would precess around the ~z axis, giving rise to a long-lived persistent spin helix (PSH), a concept originally proposed for quantum-wells of III–V semiconductors with finetuned Dresselhaus and Rashba coefficients[10,11,12,13,14,15] and very recently extended to a subclass of non-centrosymmetric bulk materials.[16]
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