Robust Topological Spintronics with Spin-Valley-Momentum Locking*

Two-dimensional topological insulators offer a tantalizing prospect that their topological edge states are spin-momentum locked, supporting the quantum spin Hall (QSH) effect. However, such QSH states are usually fragile or limited to cryogenic temperatures, which can be easily destroyed by magnetic impurities [1]. A similar situation arises in quantum valley Hall (QVH) insulators, where the resulting valley-momentum locking unlocks easily with short-range impurities and the conductance quantization disappears [2]. To overcome these challenges, we propose a planar junction formed by the QSH and QVH insulators, where the QVH and QSH edge states can simultaneously emerge along their interface, giving a novel quantum spin-valley Hall kink (QSVHK) states [3]. Unlike the single QSH (QVH) states, such QSVHK states are robust against different disturbances and imperfections, showing ballistic spin-valley-momentum locking transport even at room temperature [3]. Based on first-principles results and our fabricated samples, we show how the QSVHK states can be realized by gate control, alloy engineering, or surface functionalization in bismuthene [3]. We further reveal how the interplay between the QSH (QVH) and quantum anomalous Hall states can generate multiple Hall effects through the electric or magnetic control [4-6], where their tunable band topology can be optically probed [7]. Such multiple Hall effects are highly tunable and feasibly realized, paving an important step towards topological spintronics and valleytronics.

 

[1] X.-L. Qi and S.-C. Zhang, Rev. Mod. Phys. 83, 1057 (2011).

[2] J. Li et al., Nat. Nanotechnol. 11, 1060 (2016).

[3] T. Zhou et al., Phys, Rev. Lett. 127, 116402 (2021).

[4] T. Zhou et al., npj Quant. Mater. 3, 39 (2018).

[5] T. Zhou et al., Phys, Rev. B 94, 235449 (2016).

[6] T. Zhou et al., Nano Lett. 15, 5149 (2015).

[7] G. Xu, T. Zhou et al., Phys. Rev. Lett. 125, 157402 (2020).