Abstract
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).
Highlights
Research of novel two-dimensional (2D) materials and quantum phenomena observed in them is attracting significant interest
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 controlled by external bias voltages
The edge conductance is quantized leading to the QSH phase, which is much different from the conventional quantum Hall effect that originates from just the electron orbital quantization and Landau levels formed under strong magnetic fields
Summary
Research of novel two-dimensional (2D) materials and quantum phenomena observed in them is attracting significant interest. Numerous novel quantum phenomena have been observed in atomically thin 2D layers, such as graphene and transition metal dichalcogenide (TMDC) family. Helical edge spins in the quantum-spin-Hall (QSH) phase of 2D topological insulators (TIs) are highly important. Heavy mass of TMDC atoms provides strong SOC This SOC yields topological bulk gaps Δ in the band inversion. One of the crystal phases in TMDC family, the so-called 1T0 phase, possesses strain, resulting in the stable crystal structure This strain induces the band inversion and introduces huge, large Δ. By combining superconductors (SCs) with helical edge spin states along the sample 1D edges of 2D TIs, one can explore various quantum phenomena and realize innovative application based on them.
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