Strain-Induced Giant Topological Rashba Splitting.

Rashba-type spin-orbit coupling is an important physical phenomenon for spintronic device applications. The size of Rashba splitting is generally enhanced by increasing inversion symmetry breaking, typically by increasing the spontaneous polarization of ferroelectric materials. Here, we identify an intriguing mechanism to enhance Rashba splitting by topological band inversion induced by strain. Using density functional theory, we show that monolayer quasi-1D ferroelectric chalcogenides BaTiSe and BaZrSe exhibit in-plane polarization, giving rise to Rashba splitting in the valence and conduction band edges with a persistent spin texture. Remarkably, under 1% compressive biaxial strain, the Rashba parameter and splitting energy of monolayer BaZrSe are enhanced to ∼3.0 eV Å and ∼60 meV, respectively, among the highest in 2D materials, and concurrently, a giant Berry curvature is induced, which is ∼1400 Å in magnitude. Our analysis shows that these enhancements result from a generic mechanism of strain-induced phase transition from semiconductor to topological insulator, which in turn changes interband transitions. Our findings manifest a unique strain-induced interplay between topology and ferroelectricity, and the integration of topological bands with Rashba splitting may provide promising applications to advancing spintronics technology.