  The substrate-induced topological phase transition of silience is a
formidable obstacle for developing silicene-based materials and devices for
compatibility with current electronics by using its topologically protected
dissipationless edge states. First-principles calculations indicate that the
substrate will result in a phase transition from topological nontrivial phase
to trivial phase of silicene, although its Dirac cone is still obvious. The
substrate effect (equivalent to an electric field) annihilates its spin-orbit
coupling effect, the reason why its quantum spin Hall effect (QSHE) of silicene
has not been experimentally observed. Unfortunately, external electric field
seems impossible to recover the QSHE due to the screen effect of substrate. We
here first propose a viable strategy (constructing inverse symmetrical sandwich
structure (protective layer/silicene/substrate)) to preserve quantum spin Hall
(QSH) state of silicene, which is demonstrated by using two representatives
(CeO2(111)/silicene/CeO2(111) and CaF2(111)/silicene/CaF2(111)) through the
calculated edge states and Z2 invariant. This work takes a critical step
towards fundamental physics and realistic applications of silicene-based
nanoelectronic devices.
