  Based on first-principles calculations, we predict that the monolayer AuTe2Cl
is a quantum spin Hall (QSH) insulator with a topological band gap about 10
meV. The three-dimensional (3D) AuTe2Cl is a topological semimetal that can be
viewed as the monolayer stacking along b axis. By studying the energy level
distribution of p orbitals of Te atoms for the bulk and the monolayer, we find
that the confinement effect driven p_y^- and p_z^+ band inversion is
responsible for the topological nontrivial nature of monolayer. Since 3D bulk
AuTe2Cl has already been experimentally synthesized, we expect that monolayer
AuTe2Cl can be exfoliated from a bulk sample and the predicted QSH effect can
be observed.
