  Atomic monolayers on semiconductor surfaces represent a new class of
functional quantum materials at the ultimate two-dimensional limit, ranging
from superconductors [1, 2] to Mott insulators [3, 4] and ferroelectrics [5] to
quantum spin Hall insulators (QSHI) [6, 7]. A case in point is the recently
discovered QSHI indenene [7, 8], a triangular monolayer of indium epitaxially
grown on SiC(0001), exhibiting a $\sim$120meV gap and substrate-matched
monodomain growth on the technologically relevant $\mu$m scale [9]. Its
suitability for room-temperature spintronics is countered, however, by the
instability of pristine indenene in air, which destroys the system along with
its topological character, nullifying hopes of ex-situ processing and device
fabrication. Here we show how indenene intercalation into epitaxial graphene
offers effective protection from the oxidizing environment, while it leaves the
topological character fully intact. This opens an unprecedented realm of
ex-situ experimental opportunities, bringing this monolayer QSHI within
realistic reach of actual device fabrication and edge channel transport.
