Prediction of Two-Dimensional Topological CrystallineInsulator in PbSe Monolayer.

Two-dimensional (2D) topological crystalline insulator,a new classwhere states are protected by lattice symmetry instead of by time-reversalsymmetry, is predicted in PbSe monolayer based on first-principleselectronic structure calculations. A combination of strong spin–orbitinteraction with quantum confinement effects in PbSe monolayer leadto a topological phase transition with an even number of band inversionmomentum space points. We demonstrate that the PbSe nanostructurepresents pairs of spin-polarized Dirac cones coming from the monolayeredges, where each Dirac pair presents a unique spin alignment, leadingto a quantum spin Hall system. More importantly, due to the quantumconfinement this 2D nanostructure presents larger band gap as comparedto its parent narrow band gap trivial insulator bulk PbSe, favoringa room-temperature 2D band gap with crystalline-protected Dirac statesat the edges, turning this system interesting to combine nontrivialtopological states with nanoelectronic and spintronic applications. [ABSTRACT FROM AUTHOR]