Title: High-buckled R3 stanene with topologically nontrivial energy gap,
Abstract: Stanene has been predicted to be a two-dimensional topological insulator
(2DTI). Its low-buckled atomic geometry and the enhanced spin-orbit coupling
are expected to cause a prominent quantum spin hall (QSH) effect. However, most
of the experimentally grown stanene to date displays a metallic state without a
real gap, possibly due to the chemical coupling with the substrate and the
stress applied by the substrate. Here,we demonstrate an efficient way of tuning
the atomic buckling in stanene to open a topologically nontrivial energy gap.
Via tuning the growth kinetics, we obtain not only the low-buckled 1x1 stanene
but also an unexpected high-buckled R3xR3 stanene on the Bi(111) substrate.
Scanning tunneling microscopy (STM) study combined with density functional
theory (DFT) calculation confirms that the R3xR3 stanene is a distorted 1x1
structure with a high-buckled Sn in every three 1x1 unit cells. The
high-buckled R3xR3 stanene favors a large band inversion at the {\Gamma} point,
and the spin orbital coupling open a topologically nontrivial energy gap. The
existence of edge states as verified in both STM measurement and DFT
calculation further confirms the topology of the R3xR3 stanene. This study
provides an alternate way to tune the topology of monolayer 2DTI materials.