Title: Two-Dimensional Large Gap Topological Insulators with Large Rashba Spin-Orbit Coupling in Group-IV films,
Abstract: Rashba spin orbit coupling in topological insulators has attracted much
interest due to its exotic properties closely related to spintronic devices.
The coexistence of nontrivial topology and giant Rashba splitting, however, has
rare been observed in two-dimensional films, limiting severely its potential
applications at room temperature. Here, we propose a series of inversion
asymmetric group IV films, ABZ2, whose stability are confirmed by phonon
spectrum calculations. The analyses of electronic structures reveal that they
are intrinsic 2D TIs with a bulk gap as large as 0.74 eV, except for GeSiF2,
SnSiCl2, GeSiCl2 and GeSiBr2 monolayers which can transform from normal to
topological phases under appropriate tensile strains. Another prominent
intriguing feature is the giant Rashba spin splitting with a magnitude reaching
0.15 eV, the largest value reported in 2D films. These results present a
platform to explore 2D TIs for room temperature device applications.