  The intertwined ferroelectricity and band topology will enable the
non-volatile control of the topological states, which is of importance for
nanoelectrics with low energy costing and high response speed. Nonetheless, the
principle to design the novel system is unclear and the feasible approach to
achieve the coexistence of two parameter orders is absent. Here, we propose a
general paradigm to design 2D ferroelectric topological insulators by sliding
topological multilayers on the basis of first-principles calculations. Taking
trilayer Bi2Te3 as a model system, we show that in the van der Waals multilayer
based 2D topological insulators, the in-plane and out-of-plane ferroelectricity
can be induced through a specific interlayer sliding, to enable the coexistence
of ferroelectric and topological orders. The strong coupling of the order
parameters renders the topological states sensitive to polarization flip,
realizing non-volatile ferroelectric control of topological properties. The
revealed design-guideline and ferroelectric-topological coupling not only are
useful for the fundamental research of the coupled ferroelectric and
topological physics in 2D lattices, but also enable novel applications in
nanodevices.
