Ferroelectric manipulation and enhancement of Rashba spin splitting in van der Waals heterostructures

Ferroelectric (FE) Rashba semiconductors, a class of multifunctional materials with potential applications in spintronic devices, have attracted increasing interests recently. Herein, we employ first-principles calculations and the k\ifmmode\cdot\else\textperiodcentered\fi{}p Hamiltonian method to comprehensively investigate the Rashba effect in $MX/\ensuremath{\alpha}\text{-I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ ($MX=\mathrm{GaTe}$ and InSe) van der Waals (vdW) heterobilayers and reveal the mechanism underlying the FE manipulation of Rashba spin splitting. Remarkably, the strength of spin splitting in the $\mathrm{GaTe}/\ensuremath{\alpha}\text{-I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ heterobilayer has been significantly enhanced several times with respect to the intrinsic $\ensuremath{\alpha}\text{-I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ monolayer. This enhancement is attributed to the effective interfacial electric field contributed from the strong interfacial charge transfer and mirror symmetry breaking. Furthermore, the symmetric and asymmetric $\ensuremath{\alpha}\text{-I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}/\mathrm{GaTe}/\ensuremath{\alpha}\text{-I}{\mathrm{n}}_{2}\mathrm{S}{\mathrm{e}}_{3}$ sandwiched structures with four switchable states verify that Rashba spin splitting can be effectively tuned by the FE switch, and its enhancement is achievable if the mirror symmetry is not preserved. Interestingly, spin Hall conductivity can also be manipulated by the spin-orbit coupling associated with the intensified interfacial charge transfer. Our findings highlight the appealing potential of vdW heterostructures as an ideal platform for expanding the family of FE Rashba semiconductors and further promoting their applications in spintronics.