  Quantum spin Hall (QSH) materials promise revolutionary device applications
based on dissipationless propagation of spin currents. They are two-dimensional
(2D) representatives of the family of topological insulators, which exhibit
conduction channels at their edges inherently protected against scattering.
Initially predicted for graphene, and eventually realized in HgTe quantum
wells, in the QSH systems realized so far, the decisive bottleneck preventing
applications is the small bulk energy gap of less than 30 meV, requiring
cryogenic operation temperatures in order to suppress detrimental bulk
contributions to the edge conductance. Room-temperature functionalities,
however, require much larger gaps. Here we show how this can be achieved by
making use of a new QSH paradigm based on substrate-supported atomic monolayers
of a high-Z element. Experimentally, the material is synthesized as honeycomb
lattice of bismuth atoms, forming "bismuthene", on top of the wide-gap
substrate SiC(0001). Consistent with the theoretical expectations, the
spectroscopic signatures in experiment display a huge gap of ~0.8 eV in
bismuthene, as well as conductive edge states. The analysis of the
layer-substrate orbitals arrives at a QSH phase, whose topological gap - as a
hallmark mechanism - is driven directly by the atomic spin-orbit coupling
(SOC). Our results demonstrate how strained artificial lattices of heavy atoms,
in contact with an insulating substrate, can be utilized to evoke a novel
topological wide-gap scenario, where the chemical potential is located well
within the global system gap, ensuring pure edge state conductance. We
anticipate future experiments on topological signatures, such as transport
measurements that probe the QSH effect via quantized universal conductance,
notably at room temperature.
