Doubled quantum spin Hall effect with high-spin Chern number in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math> -antimonene and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math> -bismuthene

The discovery of quantum spin Hall effect has ignited the field topological physics with vast variety exotic properties. Here, we present emergence doubled in two dimensions characterized a high Chern number ${\mathcal C_S}=2$ and pairs helical edge states. Although is overlooked invisible chemistry symmetry indicator theory, already experimentally synthesized $\alpha$-antimonene $\alpha$-bismuthene are revealed as realistic material candidates predicted states band inversions emerging at generic $k$-points, rather than high-symmetry momenta. Remarkably, nontrivial energy gap can be large 464 meV for $\alpha$-bismuthene, indicating possibility room-temperature observation effect. Moreover, four-band effective model constructed to demonstrate further feasibility attaining this type topology. Our results not only uncover novel character antimony bismuth, but will also facilitate experimental characterization previously hidden