  We report on fabrication of a two-dimensional topological insulator-Bi(111)
bilayer on Sb nanofilms via a sequential molecular beam epitaxy (MBE) growth
technique. Our angle-resolved photoemission measurements demonstrate the
evolution of the electronic band structure of the heterostructure as a function
of the film thickness and reveal the existence of a two-dimensional spinful
massless electron gas within the top Bi bilayer. Interestingly, Our
first-principles calculation extrapolating the observed band structure shows
that, by tuning down the thickness of the supporting Sb films into the quantum
dimension regime, a pair of isolated topological edge states emerges in a
partial energy gap at 0.32 eV above the Fermi level as a consequence of quantum
confinement effect. Our results and methodology of fabricating nanoscale
heterostructures establish the Bi bilayer/Sb heterostructure as a platform of
great potential for both ultralow-energy-cost electronics and surface-based
spintronics.
