Quantum-spin-Hall phases and 2D topological insulating states in atomically thin layers

The quantum-spin-Hall (QSH) phase and its helical edge spins of two-dimensional (2D) topological insulators (TIs) are attracting increasing attention. The helical edge spin currents are a favorite to applications in dissipationless spintronic devices with low error rates because the spin currents existing along sample 1D edges are topologically protected in time-reversal symmetry and are easily controlled by external bias voltages. Moreover, combining the 1D edge spin currents with ferromagnetic or superconductor electrodes yields various exciting phenomena and those applications to innovative quantum devices. Nevertheless, reports of 2D TIs and QSH phases (particularly at high temperatures) have been rare and mainly in semiconductor 2D quantum wells. Here, I introduce and discuss how 2D TI states and QSH phases can be created and applied to innovative quantum (spintronic) devices, particularly in atomically thin layers (such as graphene and transition metal dichalcogenide family, which is energetically studied and have demonstrated large topological bulk gaps recently). Research of 2D TIs on atom-thin (or few) layers and those application must open a door to next-generation quantum architectures (such as topological quantum computation utilizing the Majorana fermion).